My XH can be similar, and he was emotionally abusive throughout our long marriage so I have had to learn not to trust him. How I cope with the headf*ck of sudden generosity (oooh, one whole night away...) is to work out whether it would benefit (a) the DC and (b) me.
And if it's yes to the first one, and as a bonus yes to the second one, then I say yes. But if it involves more than a slight inconvenience on my part then it has to be HUGELY beneficial to the kids for me to agree to it, after all he has put us through.
I also hate the whole Disney Dad shit, like he's being so generous all of a sudden when I've spent months in therapy trying to undo the damage he did, so if yours expects gratitude then he can shove it!
Re school costs, bear in mind that he can back out later as unexpectedly as he has offered it, so don't set anything up that you couldn't deliver without his help...for example if it's school fees then if he offers to pay in Year 1 then he has to follow through in future years, so you're not left with huge bills to pay if he changes his mind. Whereas if it's a school trip that you could do one year and not another, then that's more straightforward.
You also don't want to make yourself vulnerable to his manipulation ie you have to "play nicely" to get his money. I imagine it is guilt...but tough, let him feel guilty, he shouldn't have been so nasty. I can't separate my feelings from before either, my XH can appear at the door playing friends all he likes...I ain't playing!