I would vote for waiting till 1 week after release for the first roster update. If the ratings release truly reflects how the initial rosters will look then there will be problems with players being on incorrect teams. Also late signing free agents will not be on any team leading to a potential problem as to how signing them works when we open up the league.
If we do put a hold on trades and start late, I think the trade agreed upon should either be able to be reversed or changed to fit new overalls(if given). However, if the ratings stay the same, any trade agreed upon needs to be accepted like nothing happened.