1. Buttons interfaceI've choosen to buy a IPAC4 PS/2 controller board from Ultimarc to connect all the buttons I've. I go for the version 4 as I had the idea to connect more buttons in the future. This interface is very useful and easily usable.
2. Trackball / Spinner interfaceFor this, I've buyed the ME4 interface from Hagstrom Electronics. No problem at all with this interface.