Acer griseum is a fairly slow grower, and they usually look more like single trunked shrubs than trees. However, I would say it will start to look nice in 3 or 4 years (still being small of course). At that size it sure won't hurt to leave it potted up for a year or so, as long as you keep it watered.

Forget about preparing a bed and plant it in the ground where the soil is at least fairly decent and the exposure suitable (sun or part shade). Also be sure to pick a spot where you can see it during the winter.

Here is a link that might be useful: Planting Fact Sheet

I purchased a 4 ft paperbark maple 3 years ago and planted it in the center of a raised bed. It had about a 3/4 inch diamater "trunk". Now the central leader has shot up to about 8 ft but the trunk diameter is only about an inch.I hope the other branches will "fill out" in time.