On minor religions, if Shinto is included, not allowing Japan to have it as it's state religion would be ahistorical, so I think for the case of Shinto with Japan, we can allow it to be a state religion, but only if it's Japan, and only if it's with Shinto.
Idea has merit. All that's necessary is it to give a spread rate of near zero and give AI Japan a bunch of free missionaries on spawn.
Judaism giving money is little dubious.. This stereotype comes from historical reasons nothing to with the religion. Islam and early Christianity prohibited interest, were the only people who had links to the Muslim world from Europe, and also because it was illegal for Jews to own land.
Something like 5% GP rate, with 1+ unhappiness if player has state religion is better.
Orthodox can build Icon studio from SoI, holy city gives culture or espionage instead of cash. Great prophets can culture bomb. In the 600 BC start, south India should have 1-orthodox city for the st. thomas Christians, who are still there today.
Converting to Protestantism gives one free great scientist but no other bonus, no holy city. (think about it. protestant holy city?)
Muslim monastery replaced with something that gives XP or less war weariness as monasteries have never existed in Islam. No missionaries due to Arab UP applying to it.
Zoroastrianism shrine gives huge war weariness to anybody trying to invade it's owner.
Could autospread in the Roman Empire, disappears from Europe when Christianity is founded. 600 AD start it should be present in India and all of the middle-east cities outside of the Byzantines, doesn't matter to much because of Arab UP, but I always thought it should be there.
Should have at least a few wonders, there a dozens of Greek and Arab ones, 2 Babylonian ones but no Persian ones; despite UHV and that Islamic architecture was essentially based on Persian architecture.
Catholicism, probably stay as is, but it does make a lot more sense having the Pope's religion being founded on completion of the Pope-Palace.
Confucianism=stability, seems straightforward.
Sinkhism and Jainism could also give India more play choices for it's UHV.
So I'm guessing minor religions will be founded on completion of certain buildings? finally, spread-rate for all religions should be far lower, or at least follow some sort of visible logic.