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Yes, you can use them for decorating and this is actually quite popular. For help with using greenery indoors, here is more information: http://www.clemson.edu/extension/hgic/plants/pdf/hgic1753.pdf

It sounds like your holly has some kind of disease, or possibly an insect infestation. This article will give you an idea of what to look for: https://www.gardeningknowhow.com/ornamental/shrubs/holly/diseases-of-holly-bushes-pests-and-diseases-damaging-holly-bushes.htm.
Cut off the damaged parts, and try to get an analysis of the leaves and branches. You can get this from the county extension service, if you're in the US. This link will help you find the nearest office:
https://www.gardeningknowhow.com/garden-how-to/info/what-is-extension-service.htm
In the Uk, you can seek out the Master Gardeners http://mastergardeners.org.uk/get-involved/find-your-nearest-master-gardener/
or call any nearby botanical garden for assistance.

As long as it is not too cold where you are located, you can go ahead and put it in the ground now. However, for most regions it's a bit too cool for planting so I would hold off until spring. As long as the plant is not too large for the container it's currently in and if you keep it located in a sheltered location, the shrub should be fine as is for spring planting.

Though hollies are quite hardy, should you expect unusually cold weather conditions, you may want to give it some added protection (since container plants tend to be more susceptible to cold) by insulating the pot with bubble wrap (or something similar). Also, make sure that it does not dry out completely. It should receive adequate moisture through winter precip, but if it hasn't rained (or snowed) in awhile, give it some water at least once or twice monthly. For more info on caring for hollies once planted, this article will help: https://www.gardeningknowhow.com/ornamental/shrubs/holly/growing-holly-bushes.htm

There is a pest called a holly berry midge. It gets into the berries of hollies and they will not turn color when they are infested with them. I suspect that this may be your problem. This article will help: https://www.gardeningknowhow.com/ornamental/shrubs/holly/holly-berry-midge-pests.htm

This article should help: https://www.gardeningknowhow.com/ornamental/shrubs/holly/holly-bush-no-berries.htm

It means to make a partial cut into the holly piece, 4-6" above the first cut, partly to mark the butt, or bottom end of the cuttings, and partly to injure it to facilitate the formation of roots. The method described in that article, involving completely burying the cutting in the soil, is but one method of starting cuttings. For another discussion of a number of other approaches, check out this article: http://www.ces.ncsu.edu/hil/hil-8702.html