[cflsystems]

One instance of X-Payments can serve up to 10 stores. This does not mean you can install X-Payments on 10 places and connect only one store to each instance - if you do this you need to purchase 10 licenses of X-Payments...
XC stores can be installed on different servers or same server - doesn't really matter. X-Payments must be installed on separate hosting account even if on same server as XC store(s) with its own dedicated space and SSL