He sounds wonderful! I would try mainstreamed too..he will gets the best modeling kids there and the teacher can use lots of behavior modification to get him to follow rules. I would practice now and through summer to work with him on attending and listening skills and rules. transitioning to other activities ect......
A great DVD for our kids starting school and modeling what is expected is from Modelmekids called "Time for school" It is loaded with real kids and step by step the rules of school like " sitting and looking at teacher" and "standing in line", "sitting in circle time" , "listening to a story" and peer social rules and many more...it comes with a cd-rom free to print out "social stories" to reinforce the DVD... the video uses real kids to model the whole time and lots of visuals and pauses to reinforce the skill.
We used this on in our ABA program and "Time for playdate" is great for social skills like greetings,sharing, taking turns, looking, responding, what to do when others "dont" want to do what you want, ..losing..congratulating the winner..ect..Look online for website and check them out. Good luck!
I would first try mainstream with a lot of supports. The self-contained classes normally have children with all sorts of disabilities and from my experience, my son picked up a lot of nasty words, behavior, etc.