CapitalShipMaxSlotLevel is the one you want,
the base value is how much you will have period when you start the game. this is true across all 8 MAXCAPITALSHIP files. if this value is set to 1 in all 8 files, you will start with 8 crews available
the perlevel value is the amount you gain when upgrading to that level
of the per level amount in RESEARCHSUBJECT_MAXCAPITALSHIPSPHASE0 is set to 10, then you will gain 10 slots when upgrading to this level.
if you want to change them for all races, you will have to make the desired changes in:
RESEARCHSUBJECT_MAXCAPITALSHIPSPHASE0.entity, RESEARCHSUBJECT_MAXCAPITALSHIPSPHASE1, RESEARCHSUBJECT_MAXCAPITALSHIPSPHASE2, RESEARCHSUBJECT_MAXCAPITALSHIPSPHASE3.......to RESEARCHSUBJECT_MAXCAPITALSHIPSPHASE7.
its the same for the other race files.
PSI = Advent
and the number at the end corresponds to the ingame level you will be buying
RESEARCHSUBJECT_MAXCAPITALSHIPSPHASE0.entity = level 1 for vasari
RESEARCHSUBJECT_MAXCAPITALSHIPSPHASE1.entity = level 2 for vasari