Quirrell seems to be taking his teaching duties seriously, marking boring homework assignments and advising Hermione to leave Hogwarts for her own safety (though there might be other motives for that). This seems at odds with his cynical, unconcerned attitude, until you realise there was a time in canon that Voldemort wanted to be a Defence Professor.
Moody thinks rather than using a trapped Triwizard Trophy to teleport a victim (with a completely pointless return charm on it), an intelligent dark wizard would have someone simply toss the target a trapped Knut on their next visit to town. Quirrel used this exact method to take Harry to Diagon Alley (albeit consensually) earlier in the story, making this a call back (and reminder of Methods!Quirrel's genre-saviness compared to canon Voldemort).
In Chapter 74, the students who encourage Pansy Parkinson to think her soul has been eaten are all members of the Chaos Legion.
Quirrel's answer to Dumbledore after Harry killed a dementor makes us wonder why nobody caused him any problems after a Sarcastic Confession of this sort. Until we realize that the only people who would take this answer at its face value are those who know the answer to the "What lies at the center of a Dementor?" riddle, and those who had weren't likely to find Quirrel's goal in life to be all that bad.
On the same note, what everyone except Harry hears the Dementor say to Professor Quirrell is that "it knew [him], and that it would hunt [him] down someday, wherever [he] tried to hide." Harry assumes this is just something they've all constructed, rather than something the Dementor has actually said; whether or not this is true, the reader knows there's more meaning to that threat than the characters assume.
In Chapter 89, all the chracters who try to stop Harry are from the Chaos Legion, and those who help him are from the Sunshine Regiment
If horcruxes work the same way as in canon, then someone has been horribly murdered while in the presence of the Pioneer plaque and the deed has been covered up afterwards.
All of the crazy stuff Harry pulls off is done in his FIRST YEAR. What could he be capable of in his second year? The third? The fifth?
How is this Fridge Horror? If he's this awesome in his first year, think how exponentially awesome he will become as he grows up.
For that matter it's been discussed in the text.
Chapter 28, where Harry finds a loophole in the laws of transmutation to change part of an eraser to metal without changing the entire thing due to a branch of what boils down to multiverse physics. Even if it checks out on the magic side of the equation, there is no way to know what would happen once the spell wears off naturally, since it works with a probability-based science turned constant on an infinitely improbable situation, and the realm of consequence for messing with what could have been over time stretches from nothing major, to radiation poisoning, turning Hogwarts into a flaming crater, or tearing the universe atwain.
Or it could simply revert to be a normal eraser. As we can infer from the fact that the universe has not yet exploded and yet partially transfigured substances have been left lying around.
When Draco is briefly forced to consider siding with Dumbledore, he decides he'd rather be burned alive. And then when you read it again with the knowledge that Draco believes Dumbledore killed his mother by burning her alive while she slept, that comparison becomes rather horrifying.
And very similar to the decision that the Potters took — dying rather than letting Voldemort kill Harry.
In Chapter 26, Quirrel decides to take Harry to Gringotts and suggests "And we might even make it a little outing, if you like. I've just had a pleasant thought." and begins humming to himself as Harry goes. The horror comes when you reread the previous chapter and note that the last time he hummed was after resolving to "crush" Rita Skeeter. So his "pleasant thought" was actually...
The story indicates that teachers can use freely use memory charms on students without oversight or appeal (after the ritual incident, Snape modifies over a dozen students' memories without the Headmaster's knowledge). While we haven't seen any actual abuses of this, there have been tales of Defence professors who really get around or are more Obviously Evil than Quirrel, and if, like Snape, they can do it without Dumbledore's knowledge, the implications are not pleasant.
Let's be honest, Methods spends half its time examining the unpleasant implications of Rowling's magical world, such as the horrors of Azkaban, the corrupt and feudal nature of wizard society, and its distain toward non-wizards.
Those weren't "implications". They were major themes of the series.
If Harry's theory about how Fred and George pranked Rita Skeeter is correct, then Fred and George were able to False Memory Charm her and get away with it. The scale of the pranks they (or less honorable people) could effect with that method are frightening. Which, in hindsight, actually makes it a bit heartwarming that they erased the knowledge of how they did it.
Alternatively, they actually paid someone else to cast the False Memory Charm, which may mean that there is a criminal out there that does this for money. Making it horrifying again.
Given that Dumbledore 'drops' a valuable magic item near them soon after, one can imagine that HE either memory-charmed Skeeter, or faked the evidence she saw.
"Miss Granger," Professor Quirrell said gravely, "it can be dangerous to give people compliments like that when they have not been truly earned. The recipient might feel bashful and undeserving and want to do something worthy of your praise...."
And what happens in the next arc? Hermione dies horribly. Coincidence?
There are maximum two arcs left at this point, and in-universe it will all be over in two months – the end of the school year. Which means Harry will rip apart the foundations of reality before he turns twelve.
Harry keeps insisting that he has never been abused, but I do think witnessing your mother get killed and then being hit with a strong, hatefilled, dark curse that is meant to kill you but doesn't, when you are fifteen months old, qualifies as child abuse.
He gets pissed when people imply his adoptive parents are abusive. No one in story has brought up the possibility of it being what you suggested or anything else.