Don't forget about the most important element: water. Make sure you have plenty of it, and get it tested before you invest into a grow. Also make sure you get the ag test, not the drinking water test, they are different. Some elements, like boron, can be ingested safely by humans at high ppms, but will be toxic to plants.
As for soil amendment, everyone has their own mix so you will get a lot of different answers on that one. To cut costs call around and see if you can find a soil company in your area that can deliver truck loads. It is FAR cheaper buying it in bulk than in bags. This last year I bought a truckload of organic gardening soil for my plants and then tilled in some additional amendments. At $45 a yard it was no more expensive than if I mixed it myself, and it saved a lot of time.
My mix this year was an organic gardening mix made made from horse and cow manure, grape and apple pomace, rice hulls, straw, soft rock phosphate, greensand, ¼” red fir bark, sandy loam soil, crushed lava rock and a little soil sulfur. We also tilled in some additions of our own – more rice hulls, earth worm castings, and some of NCGA’s “organic magic mix” which contains myccorhizae as well as range of micro and macro nutrients that the plants will need in these first few weeks. If growing in soil be sure to use myccorhizae -they make a huge difference.
It worked well and had excellent drainage and aeration, but it could have been hotter and it was a bit low in Calcium I think. I may try a bit of guano this next year to make it hotter, and add more lime or oyster shell to increase the Calcium. On a side note - do not use gypsum for your Calcium source. It is NOT in a form available to plants and will NOT provide them with Calcium. Like I was saying though everyone has a different mix and I don't claim mine to be the best, but it did work pretty good and it was very cheap.
My other advice would be to grow either in large
smart pots (like 300 gallon) or raised beds. Both increase drainage and aeration and will help your plants grow faster. Also pick a spots that gets as much sun as possible. You cannot have too much solar exposure when growing outside. Having plenty of sunlight is one of the biggest factors for both yield and quality when growing outside.