1. Stop the GOMAD during the rehab. It is for gaining weight, not healing up an injured area. Cut down to about 1/2 gallon.
2. Depends on the injury. It might just be contused, which will heal much faster than a belly rupture and won't need a lot of rehab beyond a good warmup.
3. 20 on/20 off as much as you have time for. You can do the math.
4. Your strength will not suffer much. Minor setbacks do nothing to affect long-term progress, and they make you appreciate your healthy periods more.