markmahlum
I have grown broccoli last winter. I used 5 gallon buckets, and built the system as a drip system. The bottom third of the buckets was washed and sterilized rock, and the rest was coco chips as a growing medium. Next time I would do it more 50/50 though. By the end of the season the buckets were entirely filled with roots. In fact after it all dried up I lifted the plants by the stalk and all the growing medium as well as all the rock came out of the buckets intact. The main stalk at the base was about 4 inches wide, it was more like a trunk.

I don't know if I'm picturing your setup the way you have it planed, but I'm not sure it can handle the size of full grown broccoli plants. All my buckets had one plant in it except one had two. Combined they drank between 4 and 6 gallons of water a "day" when they were full grown. Most of the leaves got to be more than 2 feet long and a foot or more wide (not including the stem). Total the plants got to be a good 4 feet wide and about 3 feet tall.

I was using General Hydroponics 3 part "Flora series" nutrients on them. But (from my experience) I would suggest that you to grow the plants as large as you can before you try to get them to bloom. The bigger the plant the bigger the heads of broccoli, and once you cut the first head, all the rest will be smaller. The first head will come at the top of the stalk (trunk), and once that's cut it wont continue to grow upward anymore. The rest of the heads (florets) will come from side shoots, and they wont be able to get bigger than the steam of the side shoot there on.