I would use Jerry's layout for the plywood. The big box stores will even do the rips for you.
Here's how I would frame it. Let's assume you are using 2 x 4 s. Cut 2 @ 9' and 8 @ 63" (use 10' and 12' lengths). Frame the outside and then put the first cross support so it is 12" to center from one end so both sheets share it. Space the rest out at 16" intervals..
Now there are several ways to support the long seam. You can use John and Tom's method which is elegant, but they were using Mianne benchwork and you are not. What I like to do is put a 1 x 3 flat on its 2 1/2" width so it is centered 12" away from the long side and is under both long sheets. I then notch the 2 x 4 s- 3/4" deep by 2 1/2" wide so this will be flush with the top of them. You then have support the entire 8' length.
