The 1/2 will work ok given you add enough laminate on both sides of the wood. I used AC Douglas Fir 3/4 inch. As for what to put on top of the wood I used 2 layers of 1808 followed by 1 layer of 6oz cloth, followed by epoxy fairing compound.
If I had to do it all over again, I would have laid up the panels for the deck on a mold table so that way I would have saved alot of sanding.
Here's a link to my project page that will hopefully give you some decent ideas on what to do.
http://www.classicseacraft.com/forum...=&fpart=2&vc=1