Actually, let's talk about Holly. I've seen a few takes on Vecna's plan and how the whole "why Holly?" conversation seemed to be disregarded after we found out he's taking more kids.
But let's reconsider: Why Holly? Or more like, why shouldn't it be Holly?
Vecna knows who she is, she knows if Mike Wheeler finds out his little sister is missing, he'll know who took her. He also, as established by Lucas, deliberately left the rest of the family alive, even though they would be able to tell anyone, party included, exactly what happened.
He also took Holly alone that first night, even though we know he escalated immediately after and he took the rest of the children he needed in one single night. (The number of kids could be tied to convenience, but I do think Vecna has the manpower to have pulled it off in one night, if he wanted. I actually think spreading out the kidnappings is more suspicious to military and anyone else who knows what's been truly happening, ergo a bigger risk to his plan. Not that it matters to him in the end, but you see my point.)
Taking only Holly, and her first as well, leads me to believe he wanted the party to know he was on the move and he wanted to give them time to act, too. Either that or he purposefully took Holly to get to Mike.
(I think, considering his speech to Will followed by his departure and the added clue for a possible birthdaygate, Vecna does have an ulterior move that involves breaking or using Mike in order to hurt Will. Maybe the other way around, also.)
Holly being found by Max and being in on her escape plan is also possibly a danger. He knew Holly would be most likely receptive/open to Max, since they knew each other. Which is why it makes even less sense to kidnap her at all, much less first to leave her alone in the house. Unless he's using it to his advantage: He could have taken Holly first, fully knowing she would go into the woods even though he told her not to, (maybe even telling her precisely so she would go,) so she would find Max, try to escape and either A) this leads him to Max or B) Holly escapes after he's already gotten what he needs from her and he's able to use her (as a spy or otherwise) back in the rightside up. From what we saw, he's doing whatever he did to Will to the new kids, so I doubt his goal is killing them, especially since he established trust with all of them.
All to say, I think there's a reason why he took specifically Holly Wheeler, and in the way he did. I think he has something really bad planned, spanning much farther than the party expects right now. (I also think Will's powers will turn back around to putting him in danger, but that's another thing.)