John rules wise I would only limit the bps, the reason I say this is most markers have a clear setting for 15bps, I personally don't mind getting shot alot but as a coherent link between woods and 5 man your asking newer players to take alot of hits. I have seen lots of examples of people moaning about getting over shot and it's not a surprise with some of the guns set to 20bps. After playing since rule changes have taken bps from 15 down to 10.5 I feel that 15 is plenty fast enough, it will force people to actually aim there guns. If you ask alot of the x ball players(If these are supposed better players) most don't play with their bps set over 12.5 as they feel the increase of 2 is enough.
Now marshalling it everyone has to go to one crono marshal at the start of the morning or afternoon for a check, then you run on trust, if at any point a player can ask for a gun to be checked by a marshal, if it's over 15bps the team loses all the points it had up to that point.
Simple.