One cat does just fine. I have I am thankful daily that my Frog and Toad have each other to annoy. In the end it's about what you want and your resources. A single kitten can be more demanding of your time. If you feel like you're likely to get a second cat in the future a single cat is not always welcoming of a newcomer. That would be a good case for biting the bullet and getting two kits now.