Any amount for POS but more you have the more often it will pay out. But I'd say ~1000

go to Navcoin.org and download the NAVPI image this will make a bootable SDcard for the pi that you will use browser to add and maintain NAV coin.

If you have no PI experience you can order a pi with same software preinstalled from the navcoin.org store. The  software is free, but the PI costs and has to be shipped from NZ so can take a while.