Do the MIDI PRESETS have set fixed unique numbers...?? to use/reference in the MIDI Controls
No, the foot switches will select from among the MIDI presets attached to the currently selected song. So let's say you have MIDI presets with these names:
Grand Piano
Doubled Piano
Leslie
Robotic
And these songs with the presets attached:
Song 1 - Grand Piano, Doubled Piano
Song 2 - Grand Piano, Robotic
Then requesting preset 2 will select Doubled Piano when Song 1 is selected, and Robotic when Song 2 is selected.
I think I probably know the answer here and perhaps NEXT MIDI PRESET and PREV MIDI PRESET messages may be a better solution
What are the controller CCs for these?
Set List Maker doesn't define a controller number for an action. It supports certain incoming MIDI messages (including controller messages and other kinds of messages) and lets you map those to whatever actions you need, in the Settings > Remote Control window.