Mcspeed

Sterling, Jonnie gives good advise, I wouldn't touch the roots any more than necessary than to get it replanted. Only differance I would throw in is put it back into the ground or a nursery tub. Typically in grow boxes you would go to a bonsai soil, this would be ok id you shovel some up and fill in what you need around the tree to fill the box. Mother earth will take care of it for a year, better than you will ( probably) , then you can reapproach it for bonsai. Just going to have that nasty P word, you know patience.

Good Luck
Bill