How much insulin is to much to avoid weight gain?

No one answer. Everyone is is different, and it takes as much Insulin as it takes to keep sugar levels controlled. Ways to possibly reduce the amount of Insulin it takes would be to eat fewer carbs, and select carbs that have lots of fiber (whole grains, fresh fruits, starchy vegetables, beans). Strengthening exercises to build muscle mass can help improve sensitivity to Insulin as well. Check w/ your doctor.