The advice you received is pretty good. Japanese maples will grow in your area, but need some shade to do well. Morning sun and afternoon shade is best. For best results choose a type with larger leaves with broad points, rather than one with extremely finely cut, or threadlike leaves. The Emperor I variety is thus a good choice.
Mix several inches of compost into the soil in a large (10 foot wide or more) area. A raised planting bed is also good but unless the area is poorly drained is not necessary. Then dig a hole for your maple that is twice as wide and only as deep as the root ball. Unwind or cut any circling roots in the container. If you unwind them make sure and dig an extension from the planting hole to accommodate them. Don't just wind roots around in the hole.
Set the plant at the same level it was growing in the container. Put the soil from digging the hole back in firming it around the root ball. Then water it in well to settle the soil. Root stimulators are fine to use but may or may be of much benefit for the plant. Keep it on the moist side (but not soggy wet) especially during the establishment year.
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