Beds or holes in the ground filled with dirt work good depending on your drainage in the natural soil. If its hard and clay like you can get salt build up from the limited drainage. Trenches dug in rows works really well slightly pitched to one end for drainage works really good. I would go with 4x4' beds made of wood that are 18" tall per plant. Works great for monster plants.
A really simple soil mix that is super easy to work with is a 50/50 ocean forest/ happy frog mix with 3-4 cubic feet of perlite added per 100g of soil for extra drainage. This soil has a lot of great organic nutrients in it so you don't have to feed them anything for the first few weeks or so depending on how fast your plants grow. Ive always used this indoors or outdoors when I use soil with great results.
A simple soil would be the pro mix bx IMO. Good pricing on bales here and great soil.
Just as an example 1 bale costs me $23 and will fill 11 3 gallon pots. Then it's all in your nutrients you use.