Wait til March if you think it needs repotting (which means rootwork as well, in "bonsai") and do the tap in stages over a couple of years. Watch the water over winter - better to do it rarely than too often with boxwood. As far as others go, do you want to grow outdoors (only) or indoors (tropicals only), or ??? Most trees are relatively 'easy' to care for - if you know what you're doing, so I really suggest doing as much reading as possible, find local clubs to join, etc. before spending too much, so you know what you want to buy and why, and know whether you have the right conditions to grow them.