Is there a limit to the amount you can have, I know it says only one superior minion, but what about normal ones

or is it up to the gm to make up a an amount.

I believe it is up to your fellowship bonus, but i might be wrong

fellowship bonus. maybe houserule it intbonus for servitors if you heretek or warpsmith... there are som talents which can affect the numbers. also there is chance to has some horde of minions or daemon engines.

Core rules p. 137

As a guideline characters cannot have more Minions that their Fellowship Bonus, though these Minions can be of any level of power (i.e. Lesser, Normal or Greater).

Then there's this,

Tome of Excess p.52

Lord of Chaos
Tier: 3
Prerequisite: Fellowship 40, Infamy 60, Air of Authority
Alignment: Unaligned
Through dint of his fearsome reputation, prophesied destiny, or even a daemonic pact, the character can attract—and keep—a considerably larger retinue than his peers. The character may have a number of Minions equal to one and a half times his Fellowship Bonus, rounded down.