I'm in no way any kind of baby guru or even a parent but a thought occurred to me when you said he wakes the baby and then acts out. I'm not sure if the behaviour started before baby2 came around and if so my theory goes out the window. But it may have to do with jealousy over the baby. For his entire life he has had you to himself. He was your baby and if he needed something, you'd be right there. Now of course if something was wrong, you would still be there for him but he might be seeing how you rush to the baby when she wakes up he's upset because he doesn't get that urgency (because he's a big boy and can get out of bed on his own).

I remember a friend who's an older child trying to sleep in a crib again and sucking her thumb when baby2 was brought home. She didn't understand why she had to share mommy. Have you tried getting him involved with the baby? When he's acting on good behaviour explain to him about how he's a big brother and you could really use his help taking care of his little sister. He can help with things like grabbing a diaper or a new shirt. But giving him the roll as the big boy that mommy can count on to help might change his behaviour

Also I think preschool is a great idea. You sound like you really could use the break and I'm sure they are equipped to watch him. Maybe he'll get past the behaviour being with other kids

I wish you the best of luck