a lot (probably most) of rescue places recommend that cats be kept as indoor pets, what with the hazards of the urban environment, disease, malicious people, ferals etc etc
our cats are indoors cats, as we live in a 4th floor apt. they are perfectly happy, they dont scratch anything but the scratching post and they don't smell at all. Keep a few toys around for them to play with and they'll be happy. ours love the plastic rings off the 4 pint milk bottles
if you want to train them, keep a water pistol or plant mister handy. if they go somewhere/do something you dont want them to, give em a squirt. they soon assosciate that place with something unpleasant. its also funny.
litter training is simple- just put them in the litter tray a few times and away you go. cats are naturally clean and tidy, so will use it as a matter of instinct. you can even train them to use the toilet using something called a litter kwitter (no joke- my missus' friend has two cats that do this, and we are training ours)
That said, you should really get two as fenris said. If you can get 2 kittens from the same litter, then you're onto a winner. failing that, if you get two kittens they will generally adapt to each other quickly
Keeping two cats costs nearly the same (day-to-day) as keeping one for some odd reason. Dry cat food is relatively cheap (especially if you get the big sack from lidl- our cats prefer this to any other brand for some unfathomable cat-reason), and once you have the innoculations and neutering done, the vet bills are nonexistant. If you are getting a rescue cat (please, please do), they will usually be neutered as part of the 'donation' cost. You may or may not get the jabs as well.
cats make great pets and, depending on the individuals personality, become really affectionate and great companions.
