This number is not too implausible to me. I mean, I aimed for "as long as we have essence, we always have a supply of dedicated warriors ready to fight at our command". I definitely intended for Molly to expand on the paths out of hell.Then again the palace guard could have something like 50,000 royal guards in it. if we're being honest it is fucking huge after all and basically the center of world government right?
It's important to remember - escaping hells is not meant to be easy, and is always meant to be a challenge. The formal royal guard might be small, but they are super-elite. Nothing stops Molly from summoning other inhabitants of her hell. From aspirants training to join the guard, to college professors and librarians of the Infinite Library. I mean, if nothing else, I expect cyberdevils we summon to start coming from our kingdom when we get it.
I'll make another pass over the text to try and make it clear that Molly herself can in fact, call others. Should be able to, at least.
There's an upside to a relatively small number of guards - you get named characters, instead of faceless mooks.
If you mean in the world-prison buried under ice? That's deliberately left unclear. The whole thing is specifically meant to be Terra Incognita in need of exploration, conquest and restoration. But the upper boundaries could be in the trillions. I mean, it's larger than a moon. It's a multi-layered labyrinth. Even if we stipulate population density of only 1 person per square kilometer, and 1 kilometer high celling on average (i.e. assume that there are huge caverns inside), we still get 280 billion inhabitants inside.Edit: Oh by the way how many people would be in the prison minimum?