I feel that you'll need to plant both squares at the same time to make it worth your while...More squares would be even better. Yes, as soon as the radishes finish, plant that square as well.

EG

I agree with EG.

Here is a link that might be useful: Tales of a Transplanted Gardener

I want as much garden space growing things as I can possibly fit in. So, I tend to have short early season crops (like leaf lettuce) and some longer early season crops (peas and romaine lettuce), they get replaced as they finish with either more lettuce or some root crops. I continue to pull plants as their peak producing period comes and replant continually. I start some zucchini early, and some later, when I pull the first zucchini, before it gets ridiculously large and takes over the garden! I don't have a stretch (more than a week) without zucchini based on this rotation.

Getting back to your original question, I would plant no less than a single block at a time. 9 bean plants will give a nice yield, but only 3 wouldn't produce enough at once, IMHO. Definitely replant squares that are no longer producing! (oh and remember to add more compost/fertilizer when replanting!)

Most bush beans will produce all summer if you keep them picked. It will take a week or so for new flowers to form. Except for commercial use I never could understand the reason for pulling up and things like beans when with a little patience you can continue to harvest until frost. But by planting two groups two weeks apart you should not have any gaps in production.