On Q1, do you have a 'halfway house' for it? A garage is often a good choice, unheated but both warmer than outside and protected from the drying wind. It's finally become widely accepted that a tree such as yours doesn't need any light in winter dormancy, so even a dark garage shelf is fine.

On Q2, that all depends on what you intend to do with it. In general though, small cuts will heal over. Even some dead wood can look appealing with junipers, so I wouldn't worry about the cuts right now. Plus, junipers back bud well.

Of course the first goal is to keep it alive, and the research you're doing and questions you're asking say you're on the right track in that regard.

ez

I do have a garage that I could use. How long should I keep it in there before moving it outside?

What amount of light does a juniper need in the spring/summer? The only good outdoor place I can put it is on my front porch, which is covered. It will get side light for most of the day, but likely only direct sunlight in the afternoon.

The foliage on the top of the tree is pretty dense. But I have heard that you shouldn't trim in the winter. Should I wait until spring to do any trimming?

You could potentially keep it in the garage all winter. It keeps the drying winter winds at bay. A longtime bonsai enthusiast in my area keeps all his evergreens in a dark, detached garage all winter. It will need to be cold enough in the garage to maintain dormancy. Someone else may jump in and share specifics, but I know it should average somewhere around freezing.

Junipers are sun lovers, so it may end up not being the right tree for your shady environment. If you do keep it, I would be conservative in trimming. They get a lot of their moisture through the foliage, and don't respond well to heavy pruning. Take the winter to study on it. There are online resources such as cratageous bonsai, bonsai4me, Walter Pall has some good instruction, Kaizen bonsai(I know these last two have several YouTube videos as well).

Short internodes are very important in bonsai, and lots of sun is necessary to get that tight, compact growth. If you decide it won't get enough sun, and give it away but are still interested in bonsai, there are plants more adaptable to less sunlight, such as ficus.

ez