As many as you want, but we suggest each cat have his(her) own Nest. We all know a cat like to have his(her) own territory sometime, Nest will become his(her) resting spot so ideally each cat(s) have their own Nest.
This Kickstarter campaign is limited to the United States, Canada, and European Union for now, we’d love to be able to ship worldwide. However, given the size of the Nest, shipping individual units is cost prohibitive. We hope in the future to be able to get them to everyone in a more cost effective manner.
Don't see the answer to your question? Ask the project creator directly.