You have TurboCAD? I have plans for a similar idea I am doing Right now. See my post on the subject. Plywood and Pine was in my original Idea. Then I discovered the cost was almost the same for a solid wood cabinet! Of course I did find some very cheap wood. Try to fit the dimensions for the Best use of the plywood. Luan for the back would be cheaper. Just as an alternative. With 6 ft to work with, 5 shelves (counting bottom?) may leave wasted space. How tall is your average "stuff"? I settled on adjustable shelving. Probably size/size comparison of MDF vs. Ply wood. 3/4 ply would not sag quite as much as 3/4 MDF, but they would both sag @ 40" with canned goods on them. You may want to think about something thicker/stronger.
2 doors would be fine. 1 would be rather big and unbalanced when open.
My thoughts