Future Grow Garden

So i am looking into starting a garden project. I will be posting a diagram in a few when i get finished with everything i can think of on it. im looking into doing this outdoors obviously but it will be fenced off from prying eyes. my issue here is i dont want to create shade and to build extra footage would cost a lot more money just for the few feet. so here is my rough idea atm.

The area will be 18' wide, 30' long and i will be digging 6' down. for this i will be renting a backhoe so that its done in a timely manner.

This is the expensive part..... i want that area of 120 cubic yard to be filled with compost/worm casting and perlite for decent drainage. Would this be overkill? i just want the best for my babies!!! lol.

Now what im not sure about is how to build the walls (ofc i know how to make a wall) but to where there wont be any shade because with those measurements there will be a 3'x3'x6' area for each plant to grow.

Any ideas or advice would be greatly appreciated, just please dont say "this is stupid dont do it" my wife tells me that already

Are you digging down because a homemade fence is too obvious or too expensive. A fence can be as as simple as reed screens tied to an existing fence, or landscape fabric strung high. Another thing to think about is the roots won't go 6 ft down. If you get a lot of rain or humidity then there will be issues with being below grade. More to consider anyway.

Ya i live in very high humidity levels and tond of rain. How far down would be good you think?