Sounds good man. I'd take the time to focus on diet and be AGGRESSIVE with rehab like gregon said. This is crucial. You're fairly young IMO and I think your doc will recognize that and be pretty aggressive with you. If not, try and explain to the guy that your a healthy, young male that has a back round in physical activity and explain that you're motivated to get back at it. Most docs I know are usually pretty good with your wishes as long as you level with them. It's a tricky approach though, me being 20 most docs are not used to a kid trying to give them suggestions. Sometimes when I throw out a suggestion I get the "What do I know? I'm just a doctor" attitude. They're a sensitive group to say the least. I'd also recommend stationary bike. It'll be good for your head. BW squats rule and lunges as well but at the same time, don't blow this. I spent about 2 years in the hospital so I've learned to read my body fairly well. I'm hoping you can do the same so that way you'll know when you're ready to go and what your capable of doing. Just remember your still young. Let this thing heal. Rehab it properly and then when the time comes you'll be ready to get right back into it. You have to appreciate recovery, which sucks but it'll be well worth it when the time comes. You'll have great motivation built up and be ready to go hard. In the meantime, challenge yourself in others ways, diet and knowledge (reading). All the best, cheers.
Oh yeah, sit ups? Put a ban on all spinal flexion.