I have done it the last 2 years. I grew potatoes in bales and tomatoes. I threatened to do squash, but it never happened. I tried cabbage last fall but that was a complete bust. My husband didn't think the potato yield was good enough, but it was the year of the monsoon spring rains and other peoples potatoes were drowning, so I thought we were lucky to get any. The reverse is true though, you have good drainage, so they dry out faster. With tomatoes it was like growing them in very deep mulch. As soon as the roots hit the soil below the straw, the tomatoes obviously did better. I was not unhappy with tomatoes grown in straw bales. It gave me room for more plants, and they are taller to work with, like you say.

Last year I had 5 bales together with long sides butted against each other. Nothing grew in the center bale. My theory was it got too hot, so consider that in your plans. A row of bales end to end did not have problems like that. I think you could get away with rows 2 bales wide.

In my experience, the inside of the bale does not turn into compost, at least not in time to be useful. I seasoned the bales as recommended, too. My method became cut a hole in the bale wide enough for a transplant and fill it with potting soil. The roots can grow down through the potting soil into the ground below. Tomatoes can be planted lower in a modified version of planting them deeper in dirt. Alternative method is to pry the flakes apart and put a transplant in the straw. It is too hot and dry here to put 2" of soil on top of a bale and expect things to survive in it. Not even alyssum. Unless you want to water twice a day and fertilize because you're flushing all the nutrients through.

I've seen pics where everything is growing happily in the bales and flowers in the sides, etc. The only thing I can figure is it's not as hot and gets more rain.

While I didn't think they broke down into compost, the bales do deteriorate over the season. If you want to hold them together better you might wrap chicken wire around them for support.

I don't want to discourage you from trying this. Like I said, I got to grow a lot more tomatoes than I would have otherwise. I think we may have to learn to adapt the method to our climate. I will be interested to hear how squash and cukes do with this method. I may even try squash in a bale this year.