While you have some good questions here, you need to chill. Walk in there with guns blazing and it is going to backfire big time. Whoever was supervising SS6 was more than likely also supervising at least 20 other children at the time. The brutal truth here is that this level of supervision is not actually possible unless all children involved have been properly socialized.
Walk in there like you don't care about SS6's behavior and you just expect special treatment for your special snowflake and it is going to go down bad. The school decides that you are not on board with discipline and they are going to (politely) give up on him. SS6 broke a window. To put it bluntly, in school this is something that should NEVER happen. Get on board with that program and be apologetic and promise to start seeking solutions for more effective discipline and possibly therapy right now. Or you are going to see SS6 placed into a small special ed classroom and not learning shit. Very very rapidly.
Schools have very very little tolerance for discipline problems. It is highly upsetting that this is happening at age 6. You need to go in there with the right attitude. Which is not "what did the school do wrong" and is "what can we do to change SS6's behavior". If you want to keep SS6 in a regular classroom then his behavior has to be good enough to stay there. Walk softly now and be cautious. Decisions are being made about SS6's future and a lot of that is going to depend on your attitude. Can you be worked with? The school better think that is a very big, "Yes".