1. Yes you can add a spin
2. The Nacra 500 main will work but may not be optimal (this has been discussed on the forum), to make the jib work you would need to reposition the fairleads to the main beam (the 500 jib is smaller and non-overlapping).
3. There is a basic rigging guide on the performance catamaran website, and lots of rigging and tuning advice can be found by searching the forums or asking.

Good luck with your new boat.