Indoor/outdoor cat; that's fine. My first cat was that, I found him on the parking lot of my apartment development (before the days when you always needed pet deposits :-) They don't need to "go" that often. I'd still keep a litter box inside in case (after you determine whether it was ever trained by its mother to use the litter box) but I only had to change my cat's litterbox once every few months! Of course, it was down in the basement. . .

I like waiting a few months, seeing what develops (how often he wants to be in), saving up a bit of money and if someone complains or the landlord notices then give him all the money you've saved at that time (at least $25-$50) and set up a payment plan with him to pay the rest? It won't hurt to have a "cat fund" anyway, to help in case you want to take him to the vets, etc.