I think the picture on the top of the forum is geraniums but anyhow it sounds like you have some very large baskets.

You probably want to spray for insects and mildew a few times before you bring them indoors. Be prepared for a lot of leaf drop if you have a lot of difference in light conditions, temperatures, and humidity between indoors and outdoors. Some people say you can keep stress low on the plant if you acclimate it to the indoors before you bring it in for good (this sounds like a lot of work to me by taking it in and out each day for a couple of weeks).

The best thing you can do is provide a well lit area with adequate humidity and cut back on watering through the winter months. Move back outdoors next year and it should respond with lots of new growth.

What kind of spray works for mildew? Everytime I've tried to overwinter a begonia it has succumbed to mildew.

I use Neem oil but any fungicide should work. There are home remedies as well such as diluted milk, Lysol spray for mildew (this may damage some leaves), and a baking soda mix. There are some that dust the leaves with powdered copper or sulfur if you can find it.

If the leaves are real damaged, remove them and discard since they will be a source of more mildew problems. Leaves will come back when conditions are right but if mildew is allowed to spread it can kill the plant.