It definitely depends on how much you care about them. The lady from whom I got Filou -she is an animal photographer and breeds only a little had at that time 5 cats (most of them neutered) and ca. 6 bunnies (and she was writing a book about them). Her house was purrfect for the animals and very tidy and clean. For me this would have been too much work.
Here at PT there are some wonderful pet mommies like you Jen and I think everybody who saw your pictures and even more people who know you personally must see how well you take care.
And under these circumstances -if you have enough room, food, time, emotional energy -12 or even 13 will have a very good life.