Quite frankly, the power level of this PrC is, if anything, really low.

You really don't get much that is really impressive with this PrC: most of the class features are only useful from a fluff standpoint.

Let's take any of the class features that grant you "followers."

By the time you hit 19th level, the strongest of those followers is going to be 5th level equivalent.

In addition, you have restrictions on their abilities that makes them kinda useless for anything but fluff purposes. I'm not exactly sure what you are going to use your Outsiders for, since they really can't defend your plane very effectively against any of your enemies (since any enemy capable of invading your plane is probably a lot stronger than a 5th level character with levels in an NPC class.)

Plus, the services that any of your followers can give you could be replicated for 150 gp. Tops. And this is coming at a level where things that cost 1000s of gp are literally in range of your pocket change.

I mean, for a start, you could change Divine Protection to be a scaling benefit that you grant at the 1st level of the PrC, and make your Divine Realm count as one of your churches for the purposes of that feature.