BoM/TWS Message Forum

It's not on the Wiki or the interactive chapters that describe the book itself; it's mostly implied in the interactives. "Into Another's Shoes" , for example, has the implication that "a magician only has so much essentia lying around", and then suggests that there's a limit of six.

Officially, anyone can only have six golems active at the same time before their essentia spreads too thin. Stellae are (apparently) an exception, as they can somehow spread their essentia farther and can control up to fifteen. (That bit of data I can't confirm, though.) Technically, you spend your essentia on other things, but as an imprint to identify you (the Nail spell does this, for example), which doesn't count against that limit because it doesn't power or establish a connection. Golems, naturally, do - when they're active. Thus, if the pedisequos created by the regular or corpse-golem versions has no mask, and there aren't any golem-masks worn by anyone other than their creator, those connections are inactive. The moment one pedisequos or golem-mask is active, it counts against that limit.

I happen to remember the rule because it's related to how Essence works in Shadowrun. (Bti of trivia - the six Essence rule in Shadowrun was believed, in the world itself, to represent body parts - therefore, you have one Essence for your head, your torso, both your arms and both your legs. This was proven - again, in the world itself - to be false, but the limit of 6 Essence remained. The way Essence interacts with Magic in that setting is why I made that connection.)