Hiya, I'm bit curious about this combo. Evangelist is interesting because it's not the typical worshipper such as Clerics or Paladins, while the Monitor's are more appealing to me than deities, and might also work as a nice tie in to test the Mortal Usher prestige class.
What I was mostly wondering is two-fold. A) Can Evangelist pick a Monitor and gain their obedience. B) Is it far fetched to ask the DM if we could pick Evangelist, but use Monitor Obedience in place of Deific Obedience to step away from the more religious vibes and more towards an agent of cosmic balance?
Also C):
What happens if you pick a prestige class for Evangelist like the Mortal Usher, which lets you essentially gain a level in another class every two levels.
That also brings up D):
What if an Evangelist picks up Mortal Usher as the class he levels in along the Evangelist, and Mortal Usher picks Evanglist?
C & D are more of a "What if?" though, my main interest is in A & B.
You can pick any deity for Deific Obedience. Some deities qualify for more specific feats, such as Monitor Obedience for Monitors.
If you pick Deific Obedience for a deity that only has a single set of boons, then you would use that set of obediences for Evangelist, Exalted, or Sentinel boons. There is a prestige class in the Paths of the Righteous Player Companion that requires this assumption to work at all.
Between Deific Obedience and Monitor Obedience, the feat you should pick depends on what you want to use the feat to qualify for. Evangelist requires Deific Obedience, while Mortal Usher requires Monitor Obedience. I don't think you can take both feats, but I am less than 100% sure about that.
The subject of whether an Evangelist's aligned class can be a prestige class has been debated at length, with no resolution. For the Mortal Usher prestige class, the more serious issue is the multiple Obedience feats required for the combination.
For your last question, I would be skeptical of nesting the aligned class mechanic at all, much less in a circular way, but I can't point to any rules text to support this opinion.
Usher doesn't actually require Obedience, just helping a psychopomp and some knowledge skills. You might be thinking of Proctor, the Sentinel/Evangelist/Exalted version of Monitor theme?
I was considering going investigator, then perhaps Evangelist and then dip into Mortal usher. If the PrC requires 5 ranks, can I pick it at 5th, or do I have to wait to 6th? I'm thinking it can be taken fifth since Evangelist requirements are either +5 Bab or 3rd level spells (earliest at 5th) or 5 ranks in a skill.
If that's the case, I could technically go Investigator 4, Evangelist 10, Mortal Usher 6? If both pick investigator, it should be technically at level 16 for abilities, while netting me interesting abilities from both prestiges?