All the above is good advice, but to answer your question I'd suggest looking at flights about seven months out, to get a sense of routings and fares, and booking about five months out. Are all 11 people flying from the same city to France, or would you be converging somewhere? Keep in mind that it can be more efficient to fly into one city and home from another, using the "multi-city" option. Also keep in mind that the airline may make changes if conditions next summer are as uncertain as they were this past summer.
For lodging, you may not be able to book some places earlier than six months out. Do some exploring before that to get a sense of locations, amenities and prices. Refundable is definitely the way to go here if you don't mind paying more for that. With such a large group you might consider VRBO or AirBnB, or Gites de France if it works with your plans. Paris requires registration of non-hotel rentals, so look for the registration number on the listing. The advantages of a house or apartment include room to spread out, ability to accommodate different generations' sleep cycles, and ability to have some meals and do laundry "at home." Disadvantages include possible difficulty getting and returning keys, and the absence of a front desk to help with questions or problems. Hopefully you won't be changing locations too many times, keeping in mind that a group travels as fast as its slowest member.
Have fun putting this together and make sure you get credit from everybody, whether as wine or otherwise. I'd never try to pull off such a trip myself, but I'm not sure I have ten close enough friends or family anyway. ;-)