As the OP I want to thank everyone for their responses, gave me alot to consider. Don't get me wrong, we did have fun and I didn't push it to an issue - just wanted verify that I wasn't the one out of line so I wouldn't repeat the error next time if so. Overall the entire process was a bit overwhelming and frantic though.
I certainly think we'll wait to do any more until we're fairly comfortable with the rules and stats, then I'd likely be more comfortable letting them roll on their own. It really wasn't a trust thing for us since we can't tell an Eldar from a Tau yet and have to rely on people to be honest with unit stats anyway, just trying to keep up and understand what was happening.
I really liked the suggestions to just go with one or a few big units. That would have been alot easier than our many squads of little models, and left more time for visiting and gawking.
As far as how this game went, there wasn't so much teams as two groups - those you could shoot and those you couldn't. There was an attempt to select team captains but I don't think anyone stepped up to the plate. Opposing forces set up in the middle of the table w/ 12-15 players, then tyranids w/ 6-8 players moved in from the table edge. Durring each side's turn everyone moved/fired/assaulted at their own pace. Middle of I think turn three Chaos players got a free round of shooting at everyone at both sides, which I heard afterwards generated a few complaints. (since Chaos was at the other end of the tables from us we didn't even understand what was going on at the time). Certainly not very organized overall, but honestly with 20+ people I don't think one could achieve any organization if they tried so probably a reasonable approach. Game ran 4 hours for 3 turns.