Umm... I don't like to be meen but I don't think it's the best idea. Up here there not even fully hardy and all the bonsai stores, which will tell you it's ok to grow junipers inside so that they die within two or three years and you'll buy a new one, say it's not recomended you keep them inside. They need the close to freezing temps in winter and less light so if you do make it into a bonsai'ish thing then you could put it in your fridge for the winter! It's cold enough so it looses it's leaves and dosen't need light. Furthermore if it's above freezing and it gets alot of light it will be very confused and not know what to do(lots of stress trying to keep going but wanting to loose it's leaves. I'm almost positive if you leave it just on the window you'll see it deteriating and by the time
spring comes it will be very stressed.
I'm not trying to ruin your fun or anything it's just it's a deciduous
tree and needs to loose it's leaves. The best sugestion I have for you is when the temps start to drop outside put it there untill it looses it's leaves then let it have a nice sleep untill
spring when you should put it out till the leaves come back.
Bonsai isn't as tough as it may seem! Japanese maples make great bonsai and it's very fun to see that your nurturing this little life that you can hold in your hand that has all the beauty of an ancient
tree! If you decide to let the shoots grow out to five sets of leaves and then cut back to two. In a few years it will be very twiggy and pretty indeed!
The rest of Nako's advice is very good, you have to mimic it's natural environment as close as possible.
Here's some good beginer bonsai sites if your interested!
bonsai empire evergreengardenworks I personaly favore penjing the chinese form of bonsai that only uses pruning to shape the
tree but some times you have to wire a branch to get a convincing shape. If you just use the clipping methode I said about cutting to two sets of leaves then at least it will be smallenough to manage!
Good luck.