The garden/orchard here is brown clay, and here are a few things that have worked..........
The fig trees, pear trees, mulberry trees, and muscadine vines grow well in moist clay that is covered with plenty of mulch, but I still prefer to start each one above the undisturbed ground.
The peaches, plums, various citrus, papayas, paw paws, and blueberries strugggle with the clay too much, so I always plant them above the clay in very large plastic pots, in raised beds, or in separate mounds formed on top. All 3 are filled with or made of sandy, organic, rich soil mix. The blueberries are actually in giant pots filled with 50% peat moss mixed with 50% finely shredded pine bark mulch.
I don't disturb the very-packed clay when forming a new mound on top because I don't want water sitting in clay gaps, cracks, holes caused by digging a hole in the airtight, packed clay and pushing back chunks of hard clay to fill in the hole after the plant is set down on the ground. Instead, I just pour out onto the ground the contents of several bags of potting soil, composted cow manure, and the like...and mix the stuff up with shovel work. I form the round mound shape, push away the center soil to make a hole, and then set the fruit tree's root ball in that center spot after loosening the tightly wrapped roots. Since the mound will eventually settle lower, I stack the soil mix a few inches higher than the top of the root ball.
Regarding which varieties of fruit to buy and plant,I would ask you to do a lot of local studying before buying the plants. Your county extension agents, local independent nurseries, local pick-your-own fruit orchards, local individuals who grow fruit, etc. can save you lots of $$, years, and frustration by giving info on WHICH FRUIT TREES WORK WELL THERE. That is the bottom line.
National box stores are known for ordering plant inventory without care or concern about your orchard's success by shipping in inferior or 'just won't fruit here" fruit trees. Regretfully, fruit trees are persnickity. On the other hand, the best-for-your- area, high quality, productive, disease-resistant fruit trees planted correctly and cared for is a real good thing to strive for and benefit from for years. Good Luck!