The diabetes shouldn't slow you down. I wouldn't focus so much on building muscle mass though while you are tackling the diabetes. Focus on metabolic conditioning (bodyweight, calisthenics, cardio, biking, walking)
-push ups, pull ups, sit ups, lunges, whatever you like just mix it up
After your body recoups and you can absorb and digest food like a pro, then you can up the muscle. It's basically like the car engine can't process the gas. It's not so much about how much you eat but the QUALITY. You will find that in time, you will naturally be a lot less hungry after you start feeding the body everything it wants. Most of the time when people overeat, it's because we don't have the nutrition (vitamins, minerals, fatty acids, enzymes) so we just keep eating trying to get it.