As many as you can afford to feed and clean up after. But please get them from an animal shelter. I'm ashamed to say I bought my first cat (loved him, but I wish I hadn't supported the pet store.) All the rest through time have either been strays or adopted through a shelter. I got my current cat from the Humane Society on a freebie day (when they have too many cats.)
People who call others "crazy cat lady," or whatnot are afraid of someone who can love a difficult animal, maybe a seemingly aloof, aggressive animal. I take 'em like they come, claws and all. That includes humans, too. Thanks for loving cats!