1. crossfit should supplement an actual regimen if you want to compete. I have never seen a crossfiter with a balanced physique, simply because of the way the workouts are set up.
2. you will need a lot more size than you think you will need. figure girls arent huge by any means, but you would definitely give them a second look in public
3. clean bulk for as long as you can. you will need plenty of time to lean out before the show, but untiil then, pack on that size, but try not to get fat
4. cut crosssfit to a minimum. It is a recipe for back surgery. I actually work at a crossfit gym on the side (not as a class instructer, but a 1 on 1 coach specializing in hypertrophy and strength training) and I see so many people that have to quit due to back pain and messing themselves up. Lifting shouldnt be a speed based sport.