Organizing as a group as opposed to everyone booking individually has benefits. Usually, most cruise lines will give you a free berth (1 bed, not 1 cabin) for every 8 cabins booked (will vary from line to line, but this is pretty much the average). Some cruise lines will offer additional perks as well. A good travel agent is indispensable for this. My family took our first cruise last summer (when all was said and done, we were only 6 cabins........although at the beginning of planning we were at 9) and the travel agent was very helpful with everything that needed to be done.
As far as how much work is required on your part, that really depends on you. I personally did EVERYTHING for my family (because I'm the planner and they know I'll take care of everything). My agent said she could also have set it up that everyone call her individually, and just reference the group.........but you still get all the benefits.
Good luck with your planning, there's nothing like sailing with a big group of family/friends!!