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If you haven't prepped the soil with both dolomitic lime, and iron sulfate... I would go ahead and do that. Don't prune much off, as they don't usually need it. Otherwise, there is nothing more that you will have to do.

Blueberry plants are also susceptible to either iron or magnesium deficiencies.

Read more at Gardening Know How: Fertilizing Blueberries – Learn About Blueberry Bush Fertilizer https://www.gardeningknowhow.com/edible/fruits/blueberries/blueberry-fertilizer.htm

Most of the caffeine migrates to the liquid when it is brewed. However, coffee grounds should be composted before using as a soil amendment regardless of caffeine content. There are many myths surrounding the use of coffee grounds in the garden. The following article is part of a collaboration of soil scientists trying to replace the latest gardening fads with facts. Check out the links at the bottom for more information. https://www.gardenmyths.com/coffee-grounds-in-garden/

It is best to change containers right before new, vigorous growth starts, or when it is dormant. Many blueberries require extra care in container, as most are not suited for this purpose. You may Put it into a bigger container at almost any time though, without any negative effect. Here is an article that will help: https://www.gardeningknowhow.com/edible/fruits/blueberries/grow-blueberries-in-pots.htm

Without pictures it would be hard to tell. Have you fed it with anything recently? Feeding with something NOT specifically for blueberries will cause burn, if you are not familiar with nutrient requirements of blueberries.

If you have not fed it recently, it could be a more sinister issue! Fungal infections will ravage a blueberry plant and kill it very quickly. This is usually caused by overwatering, or not letting the soil dry out completely between waterings.

Please include a photo to confirm, so that I don't recommend the wrong treatment. These can be sensitive to it is important to know exactly what is going on.

Yes you can. I don't see your planting zone listed, but it's best to have at least 2 zones colder than yours if you keep the pots outside during the winter. For example, if you live in USDA hardiness zone 7, you want blueberry shrubs that are cold hardy to zone 5. If you don't have that buffer, you can move them to a protected area such as a shed or garage for winter. Here is more information:

https://www.gardeningknowhow.com/edible/fruits/blueberries/grow-blueberries-in-pots.htm