The opening battle on Cybertron shows a lot of random, generic Seekers as mooks, being mowed down en masse by the Autobots. This may be a reference to the original G1 cartoon, which tended to pad out the Decepticon ranks in crowd scenes with Starscream recolors.
The Breakfast Club is a fairly good choice for a space alien to watch while Charlie's away. It would give him a solid general overview of Charlie's social structure and a few different examples of typical humans her age, with no confusing, unrealistic concepts like magic powers.
The G1 Renditions to the Live-Action Transformers can be way off putting to some fans but this could be to illustrate that these are aliens in another world. Of course, they have to be weird looking.
Decepticons exploding when they die makes sense considering they transform into aircraft armed with missiles (jet planes and an assault helicopter respectively), so the weaponry of their alternate modes would be integrated inside their bodies in robot mode.
Optimus shows up at the end of the film. Why did he come to Earth before the other Autobots? Well, Cliffjumper got the signal from B-127/Bumblebee, so Optimus probably got it as well. Doubles as Fridge Heartwarming since he must have come as fast as he could.
If this film is truly a prequel to the Transformers film series (despite the Continuity Snarls) then it does explain a couple of things in the present day such as:
Optimus's "no hurting humans" rule: Aside from the fact that Autobots are peaceful (mostly) who only fight to defend, it's pretty much established that the reason the fight between the Autobots and Decepticons is on Earth is Optimus's fault as he sent Bumblebee to Earth to establish a base (seemingly forgetting and leaving out the fact Earth is populated with lots of living life) with Shatter and Dropkick's arrival resulting in them nearly bringing a whole Decepticon army here to kill off humanity and establish dominance on Earth, which is only halted for a measly twenty years. Its likely Optimus not hurting humans is him understanding that the least he can do for bringing his war to another species' planet is to make sure they don't end up collateral damage.
Also, according to some of the lore, the Transformers came to earth long before humans turned up. Maybe Optimus didn't note the human population because the last time any of them were there, it was nothing but dinosaurs and other smaller creatures. It also explains why he would want Bumblebee to set up a base there: he believes there's no intelligent life who could be put at risk there because there was none there the last time any beings from Cybertron were there.
Also the movie implies that the Decepticons invented the Internet to track down Bumblebee. Without it unless the Autobots had visited recently they would have little to no chance to research the planet before arrival. Worth noting here is that the frozen body of Megatron is still being analysed to develop human technology, which goes a long way to explain why two Decepticons are able to use human technology at all.
Optimus's belief in humanitys goodness: The only reason Bumblebee survived and was able to stop the Decepticons' plan was due to Charlie's compassion and courage. Something Bee likely told him all about once they met up, giving him a decent picture of humanity's inherent good nature.
Even the human antagonist changed his tune on seeing Bumblebee's heroic character, proving that, given the chance, humanity and the Autobots can be friends. And given how generally helpful Charlie (and Sector 7, once they got their heads on straight) were, humanity is also a potentially dangerous new enemy the Autobots can ill afford to provoke.
Charlie comes across as a Contrasting Sequel Protagonist to Sam and Mikaela. She has the androgynous name and Autobot in her garage, but she's also an attractive, determined brunette with mechanical skills. Mikaela was popular, while Charlie is — or has become — a loner. Charlie is attracted to a popular member of the opposite sex, like Sam, but the hot person she likes doesn't really care who she is on the inside. And Charlie spends a good chunk of the movie ignoring the Sam to her Mikaela. Mikaela knew she was hot, but worried everyone saw her as just a pretty face, while Charlie either forgot or doesn't care that she's, well, played by Hailee Steinfeld, and everyone knows who she really is, deep down. Both girls have strong bonds to their absent father who taught them how to work on cars, but Mikaela's dad was in jail, while Charlie's died suddenly of a heart attack. Mikaela manages to beat and win over a smaller 'Con, but Charlie never fights anyone directly. By the end of the first movie, Mikaela and Sam were holding hands, kissing, and in a relationship, but all Charlie gives Memo is a kiss on the cheek, and they end the movie not quite at the holding hands level. On the other hand, Mikaela and Charlie both seem to like shorts.
Why is Bumblebee called B-127 by every Cybertronian character? Because no one on Cybertron would have any concept of what a bumble bee even is, and there are only so many nouns to go around. How many other characters only got their proper names when they first arrived on Earth, with Jazz being a possible example?
Also, after being given this name, Bee insists on being referred to it even once he returns to the Autobots. This makes some degree of sense when you remember, according to the 2007 movie, Autobot is short of "Autonomous Robotic Organism". Beforehand, he was only known by a simple serial number, likely a designation he was given when created, which essentially serves as a reminder that he's a machine; by giving him a name, though, Charlie gave him an identity beyond that. She's the one who gave the Autobot his autonomy.
Charlie's bully, Tina, all but celebrates the things earlier films celebrated. She's not very detailed characterisation-wise, but she dresses in a Ms. Fanservice manner, is very sensual towards her boyfriend, and seems dismissive of Bumblebee's modest VK Beetle form, suggesting that Charlie should get a 'better one'. It helps to illustrate Charlie's Contrasting Sequel Protagonist nature as, while she does seem impressed with Bumblebee's Camero form at the end, she adored his modest Beetle form; she's also more modest in her interactions with her Love Interest, has very detailed characterisation, and though her dress sense isn't conservative (wearing mostly jean shorts), she avoids being total eye-candy by pairing her jean shorts with shirts with little to no chest exposure and wears boxer shorts under her jeans to cover more leg. The two women couldn't be more different and have a very negative relationship, which reflects the films' attempt to take the franchise in a completely different direction.
Bumblebee actually has a bit of a Non-Standard Character Design compared to the Autobot forces we see in the beginning. Besides the fact he doesn't look like his G1 self in high-res like everyone else, but the other Autobots are all carrying weapons while Bumblebee himself has them built in, transforming his arms into swords and blasters when needed and having a 'battle mask' for aid in the field. Also, while the other Autobots are all unique outside of following the same aesthetic, Bumblebee's body is near-identical to that of Cliffjumper, in a similar manner to how the Seekers all seems to have the same design too. The implication seems to be that the other Autobots were probably civilians and non-combatants who've been forced to take up arms to combat the Decepticons' forces, but Bumblebee and Cliffjumper were probably drones built for battle, reinforced by the fact Bee doesn't even have a name until Charlie gives him one. Combined with the noted above fact he can switch to 'Decepticon red' eyes when angry, the above-noted fact the Decepticon seekers similarly have cloned body models (as well as Shatter and Dropkick, who also seem to have a pretty similar body design to one-another until they scan differing aerial vehicles to give themselves different kibble) it somewhat indicates that the Decepticons' forces were inflated with machines built for the war, and likely a large contributing reason why their forces are dominating is because they're an army of clones.
In the beginning, Charlie hates getting up, she doesn't wear pajamas, is apparently comfortable hanging around the house without getting dressed (and when she has to go out to go to work, seems content just throwing some overalls over the clothes she was wearing) and when brushing her teeth she just shrugs at seeing a pimple and is seen checking to see if she has an odour, evidently to decide if she should get a shower or not (and seemingly choosing not to). Those all indicate she's not really bothered about her appearance or hygiene, which is a big red flag for serious depression. Note that as she lightens up after meeting Bumblebee, she does start wearing pajamas, and later she's fully dressed and ready for the day before even leaving her room, which likewise helps reinforce the fact Bumblebee is just a really positive influence on her emotional health.
* Hailee Steinfield's Back to Life really hammers home the parallel between Charlie literally bringing Bumblebee from the dead and Bumblebee bringing her out of her depression.
Charlie's Cool Loser status might seem odd at first; she is after-all being played by Hailee Steinfeld, a very attractive young woman, which makes it somewhat odd she's a friendless loser. However, its pretty clear that her lack of popularity has nothing to do with her looks; Memo has a big crush on her, before he even knows anything about her, indicating that in-universe she's meant to be pretty enough that boys like her before they know what she's like. It makes it clear that its not a Hollywood Homely situation, but rather her unpopularity probably just stems from her anti-social disposition and the fact she seems to be poorer than her classmates. Add in that her interests aren't very popular either (female gearheads pretty much weren't allowed to exist in the 80s), it reinforces it's due to her person, not her appearance, that she's not got many friends.
Bumblebee's eyes turn red when he attacks the Sector 7 troops, the same as the Decepticons in the film. Given how some Transformers origin stories have them as originally war weapons (particularly the Decepticons), and the statement of 'Autobot Resistance', are the Decepticons the default state of Transformers, and the Autobots are the exception to the species, not the rule?
Also note that in all previous films, the random bots created from Earth technology via the power of the Allspark were all shown to be hostile and attacked everything around them. While you could credit this to Earth tech being reverse-engineered from Megatron (meaning Decepticon tech) or assume that they were just confused and scared, it's also possible that it was just their natural Cybertronian instinct. Their default Decepticon instinct.
While the film is Lighter and Softer in its main story, the context behind the state of the Autobot forces is actually a whole lot darker. They're referred to as the "Autobot Resistance" firstly, which implies they're not so much equal sides of a war as a band of freedom fighters, making it explicit that they're completely outnumbered and outgunned by the Decepticons. Cybetron isn't dead in the film, but while ravaged by war, its apparent that the reason the Autobots left it was because the Decepticon forces had such a strong hold on it that it simply wasn't safe for them to be there and they had to abandon it. Though things weren't cheery in the previous movies, especially as time went on, it was always somewhat assumed the Autobots and Decepticons had an equal foothold and the Autobots' we saw were just a small fraction of their actual number. This time, its explicit that the Autobots are the underdogs, and they're losing.