One of the best things that you can do to increase the likelihood of success with gardens is to amend the soil to improve it. Adding and incorporating several inches of organic matter (compost) improves the nutrient content of soil, and improves drainage (or in sandy soil, improves moisture-holding capacity). Be sure to choose plants adapted to the site. For example, under the tree, use shade-tolerant plants.
I use no edging at all on my beds. I simply remove grass as it begins to creep into the bed. If you'd like an edging, choose one that you like the looks of and find affordable. Grass will eventually creep under virtually any edging material, so you'll need to do some maintance to keep beds weed-free regardless of the type that you select.