[LDiCesare]

You should not build temples in the open without a fort to protect them, even against the AI, when they border an AI province. If he invades there, you'll lose the temple. Pumping up PD there will make him look elsewhere, though.
Atlantis has a hard time getting out of water, however, and is not very efficient there, so you shouldn't worry too much.

You only need enough temples to stay in your own dominion if you've got good scales, and to make sure you are not completely overrun with black candles. The ai will not dominion-kill you. Since Man has very little in the way of sacreds, I'd probably avoid temples altogether, unless you find a fancy province like something with amazons ans want the priestesses or sacred cavalry or fliers.