I'd grow them in pots or flats. The first year they don't need a large soil mass so you can grow them closer together.
At each transplant, start sorting out the roots. If you have to choose between developing trunk/branches or roots, always choose to get the roots in order first!
Work in movement into the trunks from early on, but remember that sometimes wiring movement isn't the only way ...nor is it always the best. (Trunk chops add movement too, and sometimes its more believable.)
Gary Wood has posted a series where he plants seedlings through a tile. I know its on his blog, but I think its posted at another site as well. I'll have to dig around for it. (I know I've linked to it before.)