you need the rfx250 antenna to make the mrx1 work with RF remotes.  keep in mind that the remotes will only control the IR devices attached to the MRX1.  The remotes won't be able to work with IP, RS232, Sensors, or the relay on the MRX1.

You do need an unlock code that gets activated with the MRX1's MAC address.  This can be purchased through a URC dealer.  You only need 1 code per system.  so once you get the code, you can add as many mrx1's to the system as you like; so long as they are networked to the main mrx1.