Mel re-issued his book in 2005. On page 192, he gives the "Spacing per square foot" for each vegetable. Here are the relevant numbers:
Tomato: as a bush, 1 plant per 9 SF; as a vine, 1 plant per 1 SF
Squash (summer): as a bush, 1 plant per 9 SF; as a vine, 1 plant per 2 SF (however, my SFG experience in 2008 was 1 plant per 4 SF)
Okra: 1 plant per 1 SF
Cucumber: 2 plants per SF (I *wonder* about this one...)
Peppers: 1 plant per SF
Carrots: 16 plants per SF
Herbs: Basil (small, 4 per SF; large, 1 per SF); Chives (16 per SF); Cilantro (1 per SF); Mint (1 per SF**); Oregano (1 per SF)
Pole Beans: 8 plants per SF
**I would not plant mint in a SFG or anywhere other than a pot. It spreads invasively, like wildfire, and will take over the entire frame.
So you will are somewhat over-planted, even by Mel's own numbers. See whether you can lay your hands on a 2005 edition of his book to read the current recommendations for yourself.
I don't have feedback on most of these plants, because it's too cold at my house (due to the redwood in the back yard blocking several hours of sun every day) to grow most of the warmth-loving veggies. But I CAN tell you that Mel's recommendation of 6 inches of soil is wrong wrong wrong. You need a minimum of 12 inches, particularly for plants like...uh...carrots! and tomatoes! Other veggies have extensive root systems as well.
If you're gardening in such an intensive way--and believe me, Square Foot Gardening is one of the intensive schools of gardening--watch each plant every day for signs of harmful insects, beneficial insects, powdery mildew, and other potential discolorations. Look on top of and underneath the leaves. His book is woefully short on care of plants, emphasizing the planting and harvesting but not the in-between stuff like bugs, other pests, and diseases.
Best wishes with SFG!
Sunset Zone 17, USDA Zone
So the only ones I am out of line on are squash and okra. He changed his tune on squash, and he didn;t mention anything on okra--I just searched to see how far apart people plant seeds, and I saw 4-6"....so....I guess I'll have to watch these, and maybe they'll have to come out. We'll see.
On the comment about watching everyday for pests and diseases--is this because they are more likely to pop up in intensive gardens?