It depends upon what kind of tree seed you are using. We've only grown pine-trees as bonsais from seed. We kept the seeds cool by keeping them in the fridge for about a week after planting them, and it took about that long for them to germinate. It was a another week or two before needles started to pop out of the little shoot. It was so cute!
If you're starting from seed, it will be several years before you need to worry about trimming new growth, although depending upon the type of tree you have, you may want to "train" it as it grows.
Make sure you use "bonsai" amounts of fertilizer in the Spring and summer (growing season), and let it think it's dormant in Winter (just make sure it has enough water - many of them need to be watered every day) if you have a "seasonal" tree. If you have a tree that would be in warm wet climate, you should definitely get a mister.
Whether you keep it a work or at home, just make sure it's out of a lot of traffic. They can be finnicky about "wind." ...although the irony here is that the whole idea of a bonsai is to mimic a tree that in nature has had to battle a harsh environment - thus the "stunted" or twisted growth!
Good luck - and have fun!