Cat
Just saw your message, and I think the cukes will be too heavy to grow up the corn and pull the corn over to the ground. Bed 2 sounds fine, just remember to keep the lower growing crops, in front of the taller crops as it seems you have planned. Your spinach and lettuce will be finished for the season way ahead of the onions and carrots, so that will leave you with empty squares to plant other low growing crops. Hope all this makes sense, :)
Alberta

Cukes are very heavy, as said! And not always good viners. Better to grow them up a trellis instead of letting them pull down the corn.

Tomatoes take 2 or 3 squares, at least, IF you stake them. Indeterminate tomatoes can take over 4 or 5 squares or more. Peppers take 2 or 3 squares. Your lettuce and Peppers will be overgrown by the maters. Put the shorter things around the outside and closer to the equator (S for the north hemisphere) so that they don't get overshadowed.

If I were laying out your three 3x4 beds, I would put trellises in as many of them as possible to maximize growing space upwards and save soil space. Unless they're in each other's way, each one could have a trellis. So:

Corn = C
green leaf lettuce = L
Cucumber = Cu
Tomato = T
cayenne pepper = Ca
Onion = o
Jalapeno = l
cantalopes = cn
spinach = sp
Carrots = cr
english peas = p
cabbage = cb

^ North, I'm supposing ^

C C C
C C C
C C C
l l l
Sow your corn rows 2 - 3 days apart so you can extend your harvest while still ensuring fertilization. Interplanting with quick-growing lettuce will allow you to harvest the lettuce (maybe two lettuce crops, even!) when the corn is starting to get big, then planting more lettuce for yet another harvest or two at the end of the season when the corn is done. Lettuce growing in the heat bolts, which means sending up a flower spike and forgetting making leaves, so what leaves are left get REALLY bitter ew nasty spit. If you're in Texas, you get hot summers, so you'll be able to grow lettuce (and spinach) when it's cool in the spring, fall, and winter.

___________ Cu . Cu . Cu
Ca . . . . J
O ... T... o
o. . . . . o
Yeah, that's really a full 3x4 bed. Cukes spread out nearly as much as peppers. Kind of fudge the Tomato so it's inbetween row 2 and 3 to give it space to grow.

___________ Cn . Cn . Cn
T . . . . SP
SP . . . . T

Plant one (and only one) carrot per cinderblock hole. Can't help you with carrots, I've NEVER been able to grow them well. But I do know that one per regular cinderblock hole is a good use of space.

Your remaining veggies: peas, spinach, and cantalopes, are cool-season crops, plant them with other crops like your peppers, toms, cukes, are done and need to be ripped out.

Please note I'm in CA and can't be as helpful with TX planting as other texans, though spacings is something I'm intimately (ugh!) familiar with, as we only have half a community plot. If I were you, I'd consider how to connect these squares so they had one continuous edge, to give more planting space. Ideally, that would give you one bed 3 feet wide by 20 feet long, much more space to grow good things in!

I don't know about cukes going up corn, but you might have your peas or beans climb the corn stalks. Northeastern Native Americans used the 'three sisters' -- corn, beans and squash. Corn grows high, beans climb the corn and squash grows thick at the base. You might be able to put those in together, so your Corn squares would multitask.

Here is a link that might be useful: 3 sisters information (corn, beans, squash)