Have you considered that the cat might be bored?
If he doesnt get on with the other cats so much (my assumption as you havent mentioned their interaction with him.) then food might be the only exciting thing in his life. That and humping anything he can find!
Just think, in our modern world full of distractions, sex and food are still our (human) biggest addictions.
The same could be said for the litter box problem, once uti's are ruled out..
Picture this, the first time he might have been a bit sick, missed the box or just not reached it in time. You saw the mess and made a huge fuss. ok, it wasnt a good reaction, but it was a reaction and he got some drama in his otherwise dull life.
You could work towards making him happier by investing in a feliway plug in and by making his enviroment more stimulating with comfy perches, cat toys, a fish tank to watch and some more one on one time playing and loving on him. (One of my cats seems greedy as she is always begging by the fridge. the truth is, she isnt very food motivated but loves the interaction and the attention of being thrown food for her to 'hunt' and catch).
Playing with him more would also help him lose weight.
(I am sorry if i have got it completley wrong, i dont know you and your house could be kitty heaven for all i know
all my advice is based on assumptions)