There are two schools of thought regarding soil amendments. One says do not amend because if you add too much organic matter to the soil the roots will never venture further than the nutrient-rich area. The other advocates amending your soil with several shovel-fulls of humus-rich compost to give the young tree a head start. As long as the compost is incorporated into the native soil, the tree will be fine. Both methods work; it's a matter of personal preference.

The best amendment for soil of any texture is organic material. So if your soil is noticeably too thin or sandy, you could consider adding some rich, moisture retentive components (like peat moss and well-rotted horse manure) and if the soil is too compacted and clay-laden, add structural components (like the horse manure and humus-rich top soil).

After you plant, mulch the tree. Apply 2 inches of composted bark chips or any suitable mulch. The mulch will help retain moisture in the ground and suppress weeds. Remember not to mulch up to the bark of the tree or you'll create a damp environment that is an open invitation to pests and disease.

The vegetables in the raised beds: begin by using the right wood to create your beds. Make sure that the wood is not chemically treated making it toxic for vegetables. Cedar, redwood, and synthetic lumber made from recycled plastic work well; they resist rotting and don't require staining. 

There are many recipes for soil mixes for raised bed gardening, but it is important to remember that water will evaporate more quickly from a garden that is exposed to the air and heat on its sides. That means you will be watering more frequently and affecting the soil structure and its nutrient content in the process.

Cornell Cooperative Extension recommends you mix 1 part organic matter (peat moss, compost, etc.) to 1 part sand or perlite to 2 parts topsoil. Perlite and sand facilitate excess water drainage while organic matter helps keep an even moisture level. Maintaining high levels of organic matter is particularly important in raised beds because they dry out quickly.

As with normal garden soil, raised bed vegetable gardens require regular applications of primary and micro-nutrients. You can achieve this nutritional level through commercial fertilizers or by regularly amending your soil with organic matter, rock phosphate, greensand marl (or dried seaweed), limestone rock and other micronutrients, such as boron, that may not be adequately present in the soil.  Your preference for building the soil versus feeding the soil may vary with the scope of your garden.

pH: Different vegetables have different ranges of pH tolerance but there are few that are not comfortable between 6.2 and 6.8. (Potatoes and sweet potatoes that require pH below 6.0 are notable exceptions). This pH range is the level at which plant nutrients are most available to your plants. 

The best method to lower alkalinity in the soil is through additions of organic matter in the acidic range: peat moss, pine needles, oak leaf mold, well-aged saw dust. These amendments will have lasting impact on the pH of your garden and simultaneously improve soil structure. Quicker but shorter-lived solutions are completely fine but will need careful monitoring for changes to the pH of the soil. Powdered sulfur, aluminum sulfate and iron sulfate are all effective but should be added to the soil at different rates. Powdered sulfur requires the lowest rate of application, 1/3rd of the amount required of iron sulfate. 

I hope that is helpful. Let us know if we can be of further help.