You don't have to trim them at all - they only ever need to be trimmed for size considerations and sounds like that is not necessary here. 'Pocomoke' is a dwarf pink one.

I'm not sure what "soil prep" means. It could be a good thing (properly dug planting hole, loosening up compacted soil, etc) or a bad thing (amending backfill soil, improper fertilization, etc).

Only prune dead, diseased, rubbing, or damaged limbs. You can remove unwanted trunks (root suckers) at ground level (or below). It's best to remove them by pulling them off of the root system when they are very small (and can be pulled). This tends to discourage regrowth, to some degree. Never commit crape murder though!

In addition to 'Pocomoke', some dwarf pinkish crape cultivars include 'Chica Pink', 'Chickasaw', 'Delta Blush', 'Ozark Spring', and 'Pink Blush'. There are also quite a few that don't get a lot larger than the dwarf ones and some that are more reddish or purplish, but are still somewhat pinkish looking.