The single most important thing for your son at this age is that he can play the game with his head up and not looking down at the puck. Hopefully his roller hockey has given him that. Positional play is very different in roller vs ice, but at his age, the expectation is that he will be able to learn what coaches expect from him very quickly.
Given your parameters, the more time he can get on the ice the better. A lot of kids do privates and semi-privates to work on their skills development and it seems you have found some coaches that are providing that. Just get him on the ice as much as possible and have him play in every in-house, spring and summer program you can find.
I agree with others in that the coach is the most important thing. You need to also understand the dynamics of the team you are joining. There is no point in having your son join a team where he ends up sitting on the bench a lot. If it's possible, see if he can have a tryout period with both the teams you are considering as a practice player, purely to assess his ability to compete with the other players on the team. This would give you an opportunity to see the coaches in action and how ready your son might be for that level.
Once you sign with a team, the rules are very restrictive, but at this juncture, he's a free agent and you can play in tournaments for teams without much in the way of constraints, other than his having a USA Hockey registration afaik.
I personally would not advocate JV. The games I've seen are pretty messy due to the high variation in age and skill level.
You have a small window for pre-midget travel, and I'd recommend you jump on it, as it's going to be a tremendous learning experience for your son. If you read through the SCAHA rulebook, the various dates for roster changes metioned by other folks are listed:
http://www.scaha.com/scaha/downloads/SCAHA-Guidebook.pdf