Hello, I have built my first cabinet w/face frame for the kitchen. It has four drawers and a tall door for sheet pans, etc. I have two questions. I have BB full extensions..instructions are vague on one point, how much set-back for the slide? The drawer fronts are partial overlay. They have a 3/8" x 3/8" rabbet. Hope that is enough info. Drawers will be 18" wide, 4" to 7" deep,is 1/4 ply enough for bottoms, or should be 1/2 ply? Thanks bill