Yep, make sure he has a private space all his own. And present it to him that way. 11yo are preteen and will want their own space and time to read or whatever. And knock on the door before you enter. And don’t have the neighbor kids or your family in to party or visit for awhile. Let him exhale, a bit. Good luck.
I don’t really have any advice to give, but I think you got some good advice here. Your idea of having a game night is a good one, I agree it keeps things low key. I just wanted to say I think it’s wonderful of you for wanting to do this and it’s so much harder for older kids to get permanent placements. Good luck to all of you and let us know how it all works out.