With trees in the ground, a very thin application of compost, like less than an inch will usually be ok, when you are wanting to encourage a lot of growth, as the compost tends to have quite a bit of Nitrogen.
Adding a couple of inches of tree-surgeon mulch (fresh, shredded prunings), instead of finished compost, seems to work best, as it it more slow-release.
Natural-materials mulch of leaves and small branches also works great around trees in the ground.
About potting up, you can pot up into a container as big as you like, PROVIDED the soil mix is mostly of NON-ORGANIC materials (i.e., not decomposable, carbon-based materials): sand, Perlite, charcoal, bio-char, rock dusts, a little clay maybe, and only 5-10% by weight of slow-rotting bark or wood. Make sure the pot has plenty of holes on the lower side and bottom. Otherwise, the concerns about turning into a toxic anaerobic water rot, or low-oxygen swampy muck are very real, when you pot up a small-containerized plant into a huge container.