Ken, to answer your original question, for most cruises up to 10 days long, most cruise lines give you one free cruise berth (not cabin) for every 8 cabins you fill. If you fill 16 cabins, you get two free berths, or one cabin. Please note that these free berths do NOT include taxes, which you still have to pay, and sometimes do not include airfare even if the group has booked airfare through the cruise line.
It's up to you whether you want to organize excursions or whatnot. You can book this group through a travel agent, still earn the free trips, but not have to do the actual booking, collecting money, etc yourself. You will, however, be noted as the "group leader" and, once you're actually on the cruise, you'll be the "liaison" between the group and the cruise line.
I've booked lots of groups where the group leader asks me to escort the group, just to take care of any problems that arise. There are several different ways I can do this, one of them being that I use one of the free cruises that have been earned, but there are other ways as well. It works well for group leaders who don't, in fact, want to "take care of their every little problem and need."