The 12" deep raised bed is going to give better results - especially in the Texas heat. I'd definitely go with the 8 ft. long bed, because the zucchini will require a 2ft x 2ft space by itself - and that's with aggressively keeping it from trying to engulf everything else.
Also, you'll need at least 4 square feet of space to make growing beans worth while, and more would be even better...

Two tomato plants against a trellis at the back of the bed should provide enough fruit for the both of you to eat throughout the growing season - especially if your trellis is at least 6 ft. tall.

Most of the varieties you're considering need plenty of sunlight - although the lettuce and broccoli could definitely use a little bit of shade to keep from bolting too quick.

EG

Here is a link that might be useful: My square foot gardening blog

Thanks for the reply. Actually I'm in Birmingham--I emailed a man with Texas A&M about an article I found on the web he had written about container gardening.

I've decided to buy the Greenland Gardener sets at Sam's Club--stacking 2 of the 8x4 boxes to give me a 16" height.

I've decided to plant the zucchini by itself on a hillside that's not doing anything except growing lamb's ear and irises.

Beans will need 4 squares? Really? He doesn't mention that in the SFG book. (Just got from the library). What if I do pole beans instead of bush beans. I'm not much of a bean eater (except green bean casserole) so I don't even know if I'll like them. :-)