Your new trees can do well in pots, I have a small group of them that were novelty Christmas trees and were given to me for free and they are fine after about 5 years. Rainbowgardener is correct about not moving up too quickly, best to do it in stage otherwise the large mass of soil will stay wet longer than you would like.
I would not use a drainage layer as it does not serve that purpose. Due to water's inherent desire to cling to itself using a drainage layer will only move the damp layer higher in the pot which does not improve drainage. If you need it to keep the soil from leaking out of the drainage holes (I use screen) use a shallow layer only.
Due to the long term nature of keeping trees in pots soil collapse becomes more of an issue than it would be if you were growing annuals or seedlings that might only spend a few months in a container. To help eliminate problems with drainage and soil collapse the key thing to keep in mind is particle size. Traditional potting soils, that would be appropriate in a different situation, becomes problematic for long term use. Don't forget, you might not re-pot for 3-5 years.
I have to go now but please read over this thread and make sure to follow the links, some are dead but most are active.