I, of course, would say go for it........but, do your homework. Find a shelter who uses foster home and then TALK to these people. Most foster homes will have multiple cats. So what you want is to find a cat who has been introduced to other cats with great success. I can tell you when I bring in a new foster which ones will not cause havoc with their new adoptive siblings, and which might be more of a challenge.

As for the kitten angle, yes they are cute and playful and less of a threat to the resident cats, but oft times they are too energetic for an adult. (in other words, they can pest the heck out of an adult. And one that doesn't want to play, can get very annoyed).

Now, as for the size of the place, it doesn't sound too small for 2 cats (for 10, maybe, but not two). And don't worry about WHERE to put another box, just put it ANY where! You'd be surprised.

Most of all.....have fun choosing. It's a great time.