This can be a double edged sword, though, in that then the religion may more easily influence your realm . . . so it depends how much risk you want to take and how confident you are that you will exert more influence on others than is exerted on your realm . . . if you're confident in that, though, it is generally the way to go.
If you aren't confident that you can influence people more than you are influenced by them, then you aren't the kind of Ruler who would be working for more out-realm control than you already have, you would be working to consolidate your control in-realm...After which you could push on the religious front (grins).
If he has the opportunity to wield considerable power in the Church, yes. If he doesn't, then he's just subordinating himself to somebody outside his realm. Why admit that there is somebody in between you and the Divine Right if you don't have to?
If you can't find a way to gain significant influence within a church when you are already the Ruler of a realm and are actively working on its behalf, then either
1. You are incompetent, or
2. The Church Elders are incompetent.
Or both, of course. If the former, work on gaining competence. If the latter, have a new religious epiphany and find another religion.
