You already answered a bit of "the faith question". It's "what role should faith play in civ5" because you can't just invest something like +200 faith turn. There is simply not enough stuff. It feels a bit like gold on that part, if you have a religion up.
The main problem in my eyes is that you really use 10 GPs. In my current CEP game on speed Epic, i'm at turn 167 (95 B.C.) and i've got +102 Faith a turn. All religions got founded but only two other civs have a relevant faith/turn rate (Austria and Morocco), but both are combined less then 50 faith. I already need to spend 3.450 faith for one GP, despite having bought everything i could.
I went Policies Honor Opener, full Piety and full Tradition after that, working on Commerce right now
Beliefs are: +2 Faith from Quarries, +3 Gold for each city with my Religion (IMBA AS HELL!), +2 faith and tourism from World Wonder (got a few up with chopping), Mosques (CEP version is +4 faith, +2 culture and +1 happiness). Improvement is +500 faith from spending Great Persons (love it, super strong :>) and Reformation Belief will be the Holy Warrior-thing with "buy military units starting industrial era)
So yeah, 102 faith/turn from basically 3 cities (just founded nr 4) is super strong. I already have the most people under my doctrine. My religion has 34 cities, second one is Hinduism with 8, then Islam from Morocco with 7 and 5 from Austrias Catholicism.