WB,
OK its now the AM, got distracted by the little ones till very late.
Anyway, Pyros pretty much gave you a brief overview.
What you do is design the 1st scenario and purchase what you want the player to have for his Core Force. The 1st scenario that will be in the campaign CANNOT have any AUX/FIX units in it. They work in Scenario's BUT when slotted as the 1st scenario of a campaign ALL Fix/Aux units will be removed once the player starts the campaign. All units left alone (not Fix/Aux) will be present in the 1st scenario and these will be the Players Core Force. In a Fixed Core Force campaign I believe that the Build Points for the 1st scenario of the capaign are ignored. Support Points are available though. For all other scenario's any points allocated in the Build/Support columns will be available to the player to pick "additional" forces.
NOTE: If you want the player to have a fixed # of Build/Support points you must enter that # as a "-" then the #. Otherwise the AI will set the available points based on other variables (not sure what they are off the top of my head but I believe it has to do with battle type, points set in the preferences and a couple other factors).
All in all, I think that the Build/Support points for succeeding scenarios work pretty much the same way as in SPWAW. They are;
Build = Repair points and expand Core Force points.
Support = Support Unit purchase points.
Pyros can correct or expand on what I posted. I am stil learning alot of what can and can't be done and what affects what.