the vrs-c is for the level 1 and will not work on the level 2. anything with a -c is for level 1. anything with a -f is for level 2. anything with a -u is for elite.

you can only have 1 cpu per system.

you have a free slots for the esi & vrs.

etw phones will work fine. just remember that they connect to the black/yellow (or white/orange) pair not the red/green

dtu style phones will work IF you have a certain version of software or higher (it escapes me right now what it is).