For me the best crop to grow is pickling cukes. I wholesale them for $20 a bushel sorted by size. I retail for $2 a quart which is about $64 a bushel. I also do very well selling beans and snow peas. Snow peas sell for $4 a quart Yellow wax beans go for $2.50 a quart. Tomatillos run $2 a quart and Jalapenos $3 a quart. Good luck.
Linda

Go with what you know. Your list is good. I sell peaches and tomatoes for the most part and switch to apples and tomatoes when the peaches are done. Next year Im going to stay the same except that I am going to sell some asperigas early as a friend just bought a house with a huge patch 5 rows 100 ft long. I thought about some edible pod peas to go with that to pay the gas. I am also planting 100 raspberry plants that are fall producing because their isnt much profit in apples.

I always tried to sell what others did not have.
My hook was an open pollinated (not hybrid) long oriental burpless cucumber that tasted like a melon, loved hot weather & fruited quicker than any cucumber/melon. You'd want to trellis for straighter % of fruit that catches the eye.
Once customers bought one they became regulars!
Name translated as Suyo, Suhyo, or Soo-yoh, etc. by various seedsmen.

A successful crop, of course, depends on your growing area and market.

For $$ per square foot, those salad greens can fill the bill. They are a very labor-intensive crop, however. Not something you can grab and go, pile 'em high, and wave 'em goodbye. Nope, you gotta take them home and wash and bunch. Then keep these tender things moist and cool until they are bagged and sold. And, most difficult of all (at least, for me ;o), you'll need to do all this handling without breaking leaves and turning them into compost.

Coarse, heavy varieties would make life easier but customers are interested most in tender, baby greens. Don't even consider these salad crops unless you have handling skills for them. And then, you'll find as wide of choices as you could ever imagine.

If you live in an arid part of the world, growing can get real tough by mid-Summer but you will probably have months of quick, heavy harvest on both sides. So, don't forget to time the Fall crops.

Variety is the key for having attractive offerings. A mix of lettuces with Asian greens and scallions has real appeal. Then do it again by accurate scheduling of Fall seeding. Actually in zone 5, that might be planting in the heat of Summer in order to have time before frosts. Planting at that time of year could be real tricky. I find that Asian greens give me the best chance of greens quick enuf to beat the frosts.

You are really on the right track by thinking about greens with your tomatoes and melons. They can really "establish your presence" at the market months before you have ripe fruit to sell.

Just a quick note on heirlooms: I would use some real caution in selecting heirlooms unless you are an experienced and knowledgeable grower. There's a reason that heirlooms fell out of favor for market growers decades ago - they can be difficult to grow and ship and they are often regionally specific. In fact, that could be a definition of an heirloom - a variety that does wonderfully in one location may not "travel" well and, maybe it shouldn't travel. If you have ideas of what heirlooms grow well in your corner of the world, go for it. Those things may do real well for you in 'o9.

Best of luck,
Steve