So there are people out stealing everyone's energy... and the effect of this is to have large groups of people fall unconscious and wake up later (when the energy's returned) going "Huh, wondered what happened?" Or, more specifically, "What could cause two clowns and a dozen children to just fall unconscious in an open area?" And nobody thinks to panic over possible chemical weapon attack? At the very least, we should see some news story about a rise is gas leaks or something.
When Metallia's youma starts draining people en masse, the media interprets it as a mysterious epidemic that's causing otherwise healthy people to fall into comas. They probably applied the same logic to the earlier youma attacks, with doctors and health officials having public debates about what's causing the blackouts. We just don't see it firsthand because the story's mostly told from Usagi's POV, and the only time she pays attention to the morning news is when it's about Minako or Tuxedo Mask.
So, when Usagi gets kidnapped by Kunzite and teleported to the parts of the Dark Kingom's base they're always scheming in, the Senshi find her nigh-instantly (through what I can only assume is some form of homing teleportation). But when Ami-chan gets kidnapped in much the same way, the girls get a search montage and a bunch of "Where could she possibly be?" moments and everything! And she's walking through the city, not teleported to the heart of enemy territory. What gives?
When the villains travel back and forth between Earth and the Dark Kingdom, they leave behind latent portals that the senshi can force open, so it'd make sense if Ami blew open the portal Kunzite used to find them (since Ami hadn't gone through a portal, the girls had to search the city for her the hard way). But the weird thing is that Usagi vanished right from her bedroom: if she went through a portal at all, it should have been right there. But then Ami went running off and leaping towards the city instead, so... maybe she went to tell the other senshi what happened first? You'd think she'd just call them on her cell phone...
IIRC, when Usagi gets possessed, the girls decide that they should find Kunzite and get him to turn her back to normal. Meaning that they were probably trying to find Kunzite's hideout even before he teleports Usagi there. Also, when Usagi vanished right before Ami, Luna already felt evil energy seconds before; maybe she could somehow track down its source and give Mercury precise location of the enemy (especially since the rest of the senshi arrived right after her - we don't exactly see how they managed to find the way, so maybe Luna told them herself over the cellphones). When Ami gets kidnapped, nobody is there to see it, they simply don't know she's been kidnapped until her reappearance.
Act 25: Tuxedo Mask dies protecting Sailor Moon, and she awakens as the Moon Princess and brings him back to life with the Ginzuishou. But the exact same thing happened in the past life to Endymion and, instead of just bringing him back, Serenity destroyed the Moon and Earth. Why?
He probably wasn't really dead, just near death: just because someone's hand goes limp doesn't mean they are dead, it can just mean they passed out. Or if you're dead set on saying he really did die, maybe the power of the Ginzuishou only works on those who recently died, and we have no sense of time frame of when Serenity found Endymion dead, he could have been dead for awhile. Or perhaps she didn't have the control to focus it on healing Endymion at the time, we've seen Serenity in action, and normally her primary goal is throw a silent tantrum and blow shit up, she could have been so overcome with grief she destroyed the world without trying to revive Endymion... or maybe she didn't know it could do that. Maybe the Ginzuishou up to that point had only been thought of as a weapon, it's not unheard of, radioactive material is a real life example.
IF they were trying to present the incident at least remotely similar to how that happened in the anime version... then, in the anime, Mamoru was still alive — he goes unconscious right before Usagi awakens as Serenity, then wakes up when Serenity's tear falls on his face, and they start recalling their past — note he is still gravely injured in that version. Point is — we see pretty much the same "limp hand" scene at the end of one episode, but he is shown to be still alive in the next one.
In this continuity more than the others, Serenity and Usagi are very different kinds of people. Usagi's instinctive emotional reaction to Mamoru getting mortally wounded is a tearfully pleading "please don't die." Serenity's instinctive emotional reaction to Endymion getting mortally wounded is a blindly enraged "everyone just die." In both cases, the Silver Crystal's power made their wish come true.
So if Usagi and her past self Serenity are two different characters in this series, why is nobody else like that?
It's either because of the Crystal's connection to Metaria (so it's possible that the Serenity' essence never really left and laid dormant together with Metaria) or because Usagi has such a different personality from Serenity that her awakening gave her a split-personality.
Everyone had different personalities, but their past selves are usually dormant or overwhelmed by the current selves, with the exceptions being caused by extenuating circumstances: Beryl and Serenity were too near to Metallia, with the former overwhelming her present self and the latter causing Serenity's personality to take over whenever Usagi enters a state of shock (or allows her: Princess Sailor Moon has a much greater ability to heal people than normal Sailor Moon, but she only used it widespread in one occasion while smiling like Usagi); Kunzite and Zoisite, being the ones who saw what exactly happened at the end, were greatly traumatized, and being brought to the Dark Kingdom caused their past selves to forcefully emerge and either merge (Zoisite) or overwhelm and absorb (Kunzite) their present selves; Minako, finally, was slowly absorbing her past self, but discovering her illness caused her to give in and being partly overwhelmed by her past self until Rei's influence got her more combative present self to return to the front and overwhelming the past one to kick Metallia's ass.
This is explained in both act 0 and in the eppisode where serenity and the Ginzuishou first appears. in act 0 when Minako meets tuxedo mask she states that she remembers her past life, which explains her personality throughout the main series, in how she's focused on her mission and only occasionally has bursts of her original Minako personality (like when she teases Rei and artimus, and when usagi first transforms into serenity and reveals the Ginzuishou the other senshi bathed in the light state that the only remember fragments and feelings from their past life and not everything about who they were. kunsite is implied to be stronger than the other 3 and as such beryl has a harder time keeping him under control, while zosites loyalty to endymion allowed him to somewhat break the spell after encountering tuxedo mask and remembering the past, jadeite it is implied in the end is in love with beryl which strengthens her hold on him as well as being the youngest and least experiences of the 4, as for nephrite one could speculate that it is his hotheaddednes and impatience that makes it hard for him to recal his past life. but even so fragments of their personalities show up in their modern lives if you compare them to the flashbacks where they are shown to have the same quirks as in the past (such as mamoru not thinking his plans all the way through, while kunzite is more of the chess master and nephrite having a short temper)
Where on earth is Sailor Jupiter during Act 12. Only Mars and Mercury show up for the battle with the youma. Why isn't Jupiter called to the scene as well and why don't they explain where she is?
Was Minako's illness ever named? They don't say what it is during the episodes themselves but was it ever stated elsewhere?
It's never stated elsewhere. A tumour is the most likely suspect. In some cases the tumour must be removed with surgery and there's a 50-50 chance the operation will be fatal.