If you wish to use minions, you can either leave them unchanged from their stated abilities, gestalt them and choose their new abilities, or let the GM decide in the context of the story. If you choose your minions, and gestalt them, then you must pay the CP costs for those minions out of your own character's CP pool. On the other hand, if you leave your minions with their basic stats or let the GM decide, then your character will not have to pay any additional CP (but see 3.P Mythic House Rules).
For example, if a Wizard gains a familiar in the normal way (so the familiar isn't gestalted), then the Wizard doesn't have to pay any additional CP. If that same Wizard took the Leadership feat and gained a cohort, she'd have a choice: either leave the cohort's design up to the GM or choose the cohort's abilities and pay the CP costs. Since there are not default stats for a cohort (as there are with familiars), these are the Wizard's only two options.