I haven't had an actual garden in over 15 years and will be planting one in about a month. How large of a garden should I aim for, and how much variety should I aim for?

I have a pretty decent amount of land to put my garden on, but i'm thinking about 20' x 20' split into four cross sections. I am considering 4x 4'x4' areas so I can separate plants that do not do well together, like tomatoes from other nightshades and cucumbers. I also am planning on planting marigolds and a few raspberry/blackberry bushes (if I can get some pre-grown shrubs) between the planter areas to attract ladybugs and praying mantises to help me with my pest control. My current idea is one region with tomatoes, hungarian and green peppers, and snow peas. One area with cucumbers and cabbages for fermenting. One for sweet potatoes and melons, then one for onions, garlic, turmeric and herbs. Between each area should be probably a total of 5 raspberry/blackberry bushes evenly distributed with one in the very center. Marigolds and other flowers will be in between and help distinguish pathes between the planter regions. Sound reasonable? Thoughts?