From reading the supercell forums, it sounds like you have a chance to redesign your base between the time when a clan war is declared and the clan war starts. It also sort of sounds like they might be saved separately.
You win the war by having more stars than the other clan by the end of the clan war.
Matchmaking done on base strength (whatever that means), not trophies.
It looks like leaders/co-leaders can declare a war, so we might want to not give those roles out to everyone
An interesting quote:
Yes an equivalent number of players on either side participate. It's a 2 day process - one day to prepare one day for war, everyone gets two attacks and two defences, you cannot attack the same person twice. Choosing WHO in your clan attacks who is going to be key to win the war.
So we have a nice means to organize through this thread, which should be a nice advantage.