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While it is possible as long as the ground is still workable, it is really not advisable. The cooler temps and drier air will make it more difficult for the plant to establish a strong root system, which it would need to survive through the winter. It is better to wait for spring planting if possible. Perhaps, you could keep it in a container until then.

I do not know of uses beyond decorative, but I am not an herbalist, so I cannot say for sure.

It is too late to be planting them now. They will not be established before the winter sets in. I would recommend that you heel in the plants in a sheltered location (like near a wall or foundation) for the winter and plant them out in the spring. Here is more information on heeling in: https://www.gardeningknowhow.com/garden-how-to/info/heeling-in-plants.htm

Usually if the berries start to have problems, it is because the plant is stressed, and it is trying to preserve itself. Check to see if the plant is too dry. These shrubs require more watering during fruiting, and if they do not get enough, the plant will abort its berries. I would also check for pests that could be attributing to this as well.

You can prune off some of the branches to keep it at the shape you want; It is important to know what kind of holly you have, so that the pruning can be done at the best time. This article has more information: https://www.gardeningknowhow.com/ornamental/shrubs/holly/trimming-holly-bushes-how-to-prune-holly-bushes.htm

The answer to this question depends on what kind of holly you have, and where you're located. This article gives some basics for several of the more common hollies: https://www.gardeningknowhow.com/ornamental/shrubs/holly/common-types-of-holly.htm