I had* two indoor-only cats that I got as kittens, and I think they were fine being indoor-only. Certainly it was safer for them, especially given where we were living. (Many cat rescue groups around here won't let people adopt unless they promise to keep the cats indoors. They also tend to recommend that if you're getting kittens, you consider getting two rather than one so that they can keep each other company. But of course, that depends on the temperament of the cat: some cats do fine by themselves, and some really like having company.)

And I agree with everyone else: generally cats are pretty easy. Feed 'em daily, make sure they have water, clean the litter box reasonably regularly, and you're good. Well, and pet and play with them of course, but again, that depends on the cat. Some cats can't get enough human attention, and some prefer to hang around by themselves.

Do be prepared for a bit of property damage, though. Good furniture doesn't always survive cats.

* The cats stayed with the ex when I moved out.