I'm so glad things are still going good Lacey! I think once you get the belly issues straightened out the litter box won't be a problem. I would, however, give him another one when you let him loose. The reason I say this is because he may not want to go back to the cage for fear of being locked up again. Then again he may think that is his house and he may enjoy relaxing in there with the door open. It's hard to say but I would give him two options. I don't think it will be a problem if you do it that way.
I know you have acutally posted quit a few pictures of the little guy but if I ask real nicely can we have some more? You better hurry before sirrabed starts that darn whining!!!