It depends on how many plants you would like to have. I live inside Boston, MA
city limit, and I have a fruit/nut tree every 10ft. So in a 100ft line, I have 10 or 11 plants. I have two rows of this so I have about 22 fruit/nut trees. I like to stagger the plants so I have a 4ft gooseberry plant next to a 12ft peach tree. But mostly I try to plant dwarf or super-dwarf fruit trees vs 40ft tall
apple trees. And then along the chainlink
fence I have quite a few vines (grapes, kiwi, akebia, maypop, etc).
But to
answer your question directly I have about over 2dozen different species of fruit/nut trees in a 20ft by 100ft (2,000sqft) area. And in right infront of that is the "lawn" area. I also have some vegetable garden growing on the side of the property line and on the other side, there is some more fruit trees and flowers.
I recommend that every 10ft along the property line you plant a different species of tree, you can plant two plants in one hole or you can graft two cultivars on one rootstock (if the plant isn't self-fertile)
For zone6a, here are a few plants that you can have:
Elderberry, Jujube, PawPaw, Shipova Pear, Aronia, Seaberry, Chicargo Hardy Fig (zone pushing), Goumi, Quince (Asian & European), Pear (Asian & EU), Dwarf/Weeping Mulberry, Asian/Hybrid Persimmon, Dwarf/Native Hazelnut (esp contoured red ones), Medlar, Gooseberry, Currants, Jostaberry, thornless blackberry and raspberry, blueberry, beach plum, sand cherry, and other dwarfing native stone fruit. I dont really recommend European/regular apples and stone fruits, they are not pest resistance.
When it comes to "flowers/herbs/etc"
We have the
mint/thyme family that looks very pretty and smell very nice.
There is also the
onion/garlic family, followed by the
lovage/carrot family.
There are a lot of
edible mushrooms that will grow in the woodchip/straw/mulch that you have underneath the fruit trees.
There are some very
colorful cabbage too, plus
garden violet.