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This article may help: https://www.gardeningknowhow.com/plant-problems/pests/deer/deer-repellents.htm

The white spots could be powdery mildew, unless the white spots also have the holes in them. Then it is likely an insect problem or perhaps even a caterpillar problem. For powdery mildew, check out this article: https://www.gardeningknowhow.com/ornamental/flowers/roses/roses-powdery-mildew.htm .

Also, there is a great site to check out of finding out what insect or caterpillar might be making those holes in the leaves here: http://www.sactorose.org/rosebug/

To control the insect or caterpillar problems, a product called Sevin or one by Safer, called BioNeem is good.

If the roses are mini roses, then a pot about 10 to 12 inches in diameter should give them lots of room to grow. If regular rosebushes, you will want a pot that is 20 to 24 inches in diameter. Make sure the pots have drainage holes in them. If they do have a saucer at the bottom to catch the water, remember to dump the water out of it after 30 to 45 minutes. Otherwise it will make the root zone soggy and that will lead to alot of problems. Place the pots where they will get good morning sunshine, try to find a place where they will get at least 5 hours of good sunlight. 50 degrees is really not all that warm so they should do fine.

This article may help: https://www.gardeningknowhow.com/ornamental/flowers/roses/roses-planted-containers.htm

Unfortunately, yes, the tree rose is finished. Tree roses are built or grafted. When the get broken or the top part dies, you are left with the cane stock that formed the "tree trunk" part of it. Here is a link to an article about tree roses, many folks do not know the truth about them and have the same thing happen that has happened to you. Link>>: https://www.gardeningknowhow.com/ornamental/flowers/roses/learn-more-about-tree-roses.htm

Those little pests are likely a form of caterpillar and they do indeed have amazing appetites. You can spray your rose bushes with an insecticide such as Sevin or BioNeem (neem oil). Follow the directions on the label and most likely two applications will be required. There can be several cycles of the caterpillars hatching out from the eggs layed by moths in the garden soils. So even when you think you have gained control, keep an eye on things for several weeks. At the first sign of any damage, re-spray to help keep them from getting ahead of you.