spinach, pak choi, and arugula should be fine as long as the pot doesn't get too hot. Most leafy greens have shallow roots. I wouldn't bother planting peas in it.

This might help: http://farmflavor.com/gardening-tip-know-your-roots/

That link was what I was looking for. Thanks bardamu!

If you like snow peas, there are some early varieties that don't grow but about 2 feet tall. They would probably work. I think burpee has a carrot called little fingers that can be planted one inch a part, great container carrot, and then one called short and sweet. I think it's a 3 inch carrot. My experience with edible pod peas is that they put on from the bottom up, so you may find that you could get a bit of a harvest before they got root bound. In my area, the heat gets to peas before they would naturally peak out, So I often just get a few pickings. Zone 6 probably is better for peas.

Sure, you can plant any and all of them in 7.5" deep soil, as long as they are watered and fed. That includes peas too.