Pretenders make three temple checks, one with 100% success chance. Disciples make 1 temple check. Priests only spread dominion if they're set to "preach", I think (disclaimer here) that the success chance is X*30%, where X is the holy level of the priest (so lvl3's always succeed).
1. Hydras are bit of a trap unit anyway. They are extremely expensive for a unit, and despite high hp + regen, they don't have much defence or protection to tank hits. In addition their poison aura doesn't really synergize with your human troops until you can research poison resistance buffs much later. They probably have a niche use, but you definitely overspent on them this game. Gold for gold basis, you could get 16 high quality legionnaries or 3½ serpent cataphracts instead of a hydra, and either would be much more versatile.
2. Diplomacy is the key. It won't always save you but I'd say it's a self-imposed challenge to play without diplomacy in a match like this.
3. Wars on two front should be avoided. That's really all that needs to be said on that.
4. Some players have differing opinions on the matter: others expect you to fight to the last by yourself. Others are ok with people turning into kingmakers once they lose a realistic chance at winning the game. I haven't played enough to pick either of those opinions as my own just yet. In either case you should still have some strength left. If it's easier for me to grab your cap than it is for me to write you a reply about some alliance, I'll probably do the first.
Glad you enjoyed yourself, hope to see you in another game