Hi,
1) If the same SFTP/SSH server (same configuration, same set of users, same keys, and so on) is supposed to be accepting connections at those ports, use a single instance of FileServer and bind it to all the ports you need. You would not gain any performance improvement if you created multiple FileServer instances for this purpose. On the contrary - by using a single FileServer instance, you actually save a bit of memory and other system resources.
2) There is no built-in limit. The component will keep trying to accept more connections until it runs out of resources. If you would like to limit this yourself, it's possible to use events such as Connecting, Authentication or Disconnect to keep track of active sessions and limit accepting connections as needed.