Dimension Blue is a S. nemerosa form, and will do better in the sandy portion of the garden. Be easy on yourself, since you are just starting out.

You will learn that native soils need to be developed, which means incorporating humus to build up mitigating conditions that allow for a broader range of plants to be supported.

A handful of compost for a half-gallon plant is not enough. I'd dig a hole three to four times the volume of the plant, and half fill it with humus, then blend that with an equal volume of native soil, set the plant, and cover to about a half inch below the soil level to allow water to collect.

Later, try a raised bed made with sandy loam, with added humus. Certain mulches decompose to a nice humus, especially partially broken down hardwood bark (not shredded wood, which is mostly cellulose)

Loostening the roots of a dense root ball is usually a good idea.

You didn't mention your USDA plant zone, and your location, since the latter is a clue to your climate. There is a big difference between the xeric southwest and the subtropical southeast, for example. Soil pH is another factor.

I would not plant within the drip line of a tree, which is the boundary under shade that stays dry after a brief shower. The tree puts out stabilizing roots there to keep it upright in wind. Maples are surface feeders, and are more avaricious than other trees. I also would be careful planting annuals and perennials near hardwood shrubs. The latter also have very competitive root systems.

I am in zone 4, Wisconsin. Where I have located the salvia is a raised bed that I created behind a new garage that I had built last fall. The contractors had huge mounds of sand and sod that had been bulldozed there during construction and then left there. This is why part is more sandy and part more claylike. I flattened the mounds with my tiller, mixed in some compost, and put landscape edging around it. There is a huge old maple tree about 20 feet away and a large old lilac bush at one end of the bed. Hopefully the salvia will do well there. Thanks so much for all the tips and encouragement!