Tried it again last night! I think I have it perfected
Double pantheon trick: if you have a nice pantheon (Poland is esp good with this since they open tradition/piety hybrid pretty well) you can double its effect with religious tolerance (open tradition and you may choose to take the free monument or not, up to you, but I would rush to piety to get my pantheon going... then once you get a religion it is a very easy 2 policies you can afford in piety, and then you can get the +2 food and +happiness from tradition as usual by medieval or so)
Your pantheon counts as a "majority religion" for religious tolerance and so cities that are still majorly pagans (follow your pantheon) will double its pantheon effect once your religions starts spreading there. The best way a lot of times is to make one of your satellites (preferably the one that does not really receive a lot of bonuses from the pantheon) the holy city instead of your capitol, then your capitol (and other cities which were founded BEFORE your religion so they will start off being pagans... sometimes you can delay founding your religion for this) gets double bonuses, which can be game breaking: +2 faith from desert, +2food from whatever, +8 faith from natural wonder, etc. This is especially hilarious with +4 faith tiles (quarries or gems/pearls) and holy warriors.
If anything else, the worst case is double god-king which is pretty good early game.
The bonus wears off once pantheon is no longer the majority religion so be careful!
Here you see Poland with double Sun God (flood plains wheat with +8 food), I founded my religion away from my capitol, and used a caravan to get one follower. Getting 32 food and 5 hammers from 5 tiles worked is amazingly effective
Beelining theology (shortest way to medieval) is a good bet for finishing piety on time for 5th religion AND by doing so getting a reformation belief to boot! Here I opened tradition as well.