Ace is going to be a great brother. I am sure he will be jealous occassionally, I'm sure he'll want to be the center of attention and not sharing it, and I am sure he will act out that he is not the only kid in the house anymore - but I think for the most part he is going to be a very loving and protective older brother.
As of late he has wanted baby Mae to come out so he can hold her. So we've substituted baby with Tigger and 'practiced' holding baby sister. He also likes to touch my stomach and feel the baby move. It's really sweet and makes me so happy he's excited for his sister to be here... even if he doesn't totally understand what that will mean for his world entirely. :)