Re: Deck Cleats?
The cleats are only really necessary if you think it'll be hard to hit the 3/4" edge of the stringer plywood w/ a deck hold down screw OR you don't want to put ANY screw holes in the stringers at all to hold down the deck.
I'd wrap your stringers 1st completely
Wrap the cleats 2nd, before you install them
Install the cleats using PB & clamps (no screws)
This ^^^ isolates the cleat from the stringer, so IF there's water intrusion because of a deck hold down screw, it's ONLY into the cleat. Then if the cleat fails after becoming water logged, there's a hope that the stringer is unaffected, allowing you to remove the cleat, rough & scuff the stringer and re-install a new cleat.