I've ridden in large groups and organized smaller groups (30 or few bikes). The smaller groups I know the people and know their abilities. I've seen really stupid riding in the large groups. These are usually rallies or charity rides. It is more nerve racking in a group and you must be alert of everything around you, but there is the added safety of not worrying about cagers as much. Though proper distance is required. Don't be so scared to keep so far back as that's an invitation for a cager to try to cut in. You should be no closer than 2 seconds behind the bike in front of you and no closer than 1 second to the bike diagonally from you, the later is more important IMO. Maintain as consistent speed as possible. Don't be one of those people that speeds up, slows down, speeds up, its annoying. I doubt in large groups they'll be using more than left and right turn hand signals as many of the people on the ride won't know the other signals. When I was the president of a star chapter, I made sure we had a safety briefing before every ride (especially when there were new riders with us), reviewing the rules, the hand signals etc. I've never seen this safety briefing with larger rides.