I think you should take as long off as you need. With me, I planned on starting in October simply becuase everything works out that way in planning. Everything blends nicely and falls right into place, so that's how I determined my start date. One thing you could try is giving yourself a certain amount of weeks to work with for indoor and outdoors and plan backwards that way to get a starting point. That's what I did.
Otherwise, I think 12 weeks is fine. Most (aka CF followers) don't advocate more than 3 weeks off, but I think that becuase you run yourself into the ground for 8-9 months a year, taking off a couple can only help.