I'm okay with the reset. It gives us a chance to answer the question: Could Vanya have been saved? If RH hadn't been a horrific "father". If Allison had explained things better. If Luther hadn't locked her up. If the siblings had overruled Luther. If they hadn't rushed her on stage. She did many horrible things, as a child and as an adult. Maybe that's just who she would always be, out of control, vengeful, self-centered, and she had to be neutralized. Or maybe not!
Without a reset, we basically have Vanya the Villian up against her siblings and that's not that interesting to me. Even if they'd stopped the apocalypse then what's there for future seasons except fight after fight? Not seeing the point of that. Interesting that the apocalypse still happens, just differently.
As many have said, Vanya was treated badly by RH but not necessarily worse than the others so that's not an excuse to be homicidal. OTOH, when Allison was watching the surveillance videos she noticed how the siblings behaved towards Vanya and said if anyone had treated her daughter the way she'd have gone ballistic. This may have been a lousy writing choice, telling instead of showing, but if Allison's observation can be trusted then maybe I have a little more sympathy for Vanya.
I really, really want to know the backstory of Reginald. At first glance it looked like alternate Steampunk timeline (Victorian + rockets) or post-apocalypse future, but can't reconcile "future" if literally everyone was wiped out in 2019. (Which, that's a whole other thing. How does everyone get wiped out and yet leave a hospitable environment for Five?) Being from another planet, either as an alien or returning from a human colony, makes more sense. The firefly-magic release felt like he created the superpowered children. But that was like 70 years before they're born, so ?
About all those extra kids...how could RH be so sure Leonard WASN'T special? (Reminded me of Syndrome going villainous due to rejection by Mr Incredible.) There were possibly more superpowered kids running around in the world. And not necessarily only born on that day, either. If magic kids are possible then more magic kids are possible. The best explanation I have for why he was able to buy 7 children is that none of them planned those kids, and they weren't even pregnant more than a few hours. I can see why those parents would be much more willing than usual to sell their kids. It's not really their kid. The fact that 40 kept them and they aren't all locked in up a science lab is the bigger mystery.
I think the numbers did mean rank order. No idea how that translated to the pram numbering or at what age that becomes set in stone, but they do seem ordered by priority/power -- Luther, Diego, Allison, Ben, Five, Klaus, Vanya. At the end, Diego challenges Luther's leadership and says if he wants to be/stay #1 then he needs to lead. Luther didn't have any obvious powers that I saw (I'm assuming strength) but he did seem to be treated as the "eldest". I had a hard time remembering they are exactly the same age!