I ditto the vet visit-it's a very good idea to take them in when they are healthy and you just bring them home-to get a baseline and to make sure everything is good
I'd introduce parsley, cilantro or romaine first

They seem easy on tummies and a big favorite in most bunnies. A good thing to know is almost all rabbits turn their nose up at something new for the first few tries. So put a few sprigs of parsley down and expect to remove them the next day, repeat and in a few days your bun might taste them
Alfalfa is fine as a treat-and if he's never been given hay I'd start with an alfalfa/tim mix as that might entice him to try hay
Kudo's on taking this guy on-and ditto I'd love to see pictures and read updates as you go
