in each tribunal, each player may have 1 magus "free"
additional magi require the player to have a number of companions greater than the number of magi they have
for each "free" magus, players may create one "free" companion
to create additional companions they must have at least 3 more grogs than 3x the number of companions that they have.
grogs do not need to be actively played- they can be put in covenants in the same roles as specialists, to provide background skills or improve the covenant's economy
grogs which are played can become promoted to companions through play through a combination of gained signifigance and gaining virtues beyond the initial 3 minor virtues- both are necessary, simply gaining wealth through work is insufficient
companions may be raised to magi or magi equivalent through game mechanics- either having the gift, being opened, trained and passing the gauntlet or by gaining 2x the value in virtues hey have in flaws (and becoming a mythic companion)
whenever a character is retired they may be replaced with another character equal to their finishing level, regardless of the above rules.
The exception to the above rules are mages in the Theban tribunal, when they begin as apprentices being selected and are effectively in the magus category to begin with, despite being created with companion rules.