1974 20' Questions for Those Who Have Gone Before

[Normagain]

I'm getting ready to redo my deck and transom, and have a few questions for those who have done this.

First, is 5/8" plywood sufficient for the decking? I'm planning on using the Joubert Okoume plywood which apparently is the very best with 11 ply and somewhat lighter than Aquatek. I believe I used 1/2" cheaper marine grade for a 60's 15' Cobia I did before but I also glassed both sides of the plywood and foamed in the entire under deck to give it more strength. That puppy was strong! I do plan on glassing both sides of the plywood but foregoing the foam on this boat since I want a nice bilge.

The second question is, for rear scuppers to be above the waterline, how many inches should the deck be raised?

Thank you in advance for any help!