Serviceberries need to be pruned annually, so remove some old bark, overlapping branches, etc. You may also prune them to fit your liking, as they are generally ornamentals. Hope this helps :)

It generally depends on the species - some Amelanchiers are very shrub-like with multiple stems and a few even have a suckering, spreading habit. Others are more tree like with a single trunk.......frequently these are selections of the hybrid x grandiflora.

I wouldn't attempt to prune one into something it is not. Even the more shrubby species will eventually attain an appreciable size and all will produce fruit, although some species and cultivars larger and in heavier quantities