For your stand, which is the top? I'm confused about the bracing you mentioned, where you planning to put it. I've built few stands myself and 2x4 was choice for support. The lumber choice you are using is great, but again, if the top is the first pic, then I'm concerned about the ends/sides not having proper support. If it is turned to the side, then the sides may have enough support. Make sense?
~Matt