My Tommy has been diabetic in a free feeding house (with 5 other furry residents) on 2 injections per day since about 2004/5.
I have found that it helps to have meals and Tommy's injections at set times, as much as possible, every day. In addition to this, because my partner and I work full time, I have to make absolutely sure Tommy has eaten enough before I give him his morning injection and leave for work. On some occasions, this may mean that I have to offer him a second or third bowl for breakfast, if the first ones are not to his liking, and admittedly, this can take some time. I also tend to run around putting everyone's food bowls in front of them, wherever they are, so that they don't try to steal any of Tommy's.
My vet supplies me with disposable syringes for Tommy's injections. As I am an insulin dependant diabetic myself, I asked the vets about pens for cats only last year, but they said that these aren't available yet.
Tommy does like to try to sneak away before getting his injection, but he is a very good cat, and I can usually persuade him to sit or lie down after he has finished eating, and it is no problem to give his injection then.
When he was first diagnosed, Tommy initially took about 3-4 months to stabilise on the correct insulin dose for him, and my vet took the decision that Tommy would have to have the correct dose for his lifestyle, rather than imposing a diet on him which there was no way of ensuring he would adhere to. We seem to have done OK on this so far.
I see no reason why Boots shouldn't join your family, it sounds very like mine, and I think he looks adorable
If I have been too vague about anything, then please feel free to ask about anything.
Wishing you & Boots the very best of luck with your OH tonight.