I overwinter mine in the basement every year, under grow lights. These are fibrous rooted begonias, so not really conducive to storing dormant. I always cut mine back to about 8 inches and let them regrow. IMO, unless you have extraordinarily bright indoor light, they are going to suffer a lot of transition stress and just drop the blooms and much of the foliage anyway, so it's easier and yields a better plant in the end to just go ahead and cut them back.

It definitely wants as much light as possible, so a large south doorwall would be great. You can add a florescent spotlight if necessary to augment the natural light, and it should bloom all winter for you.

They're actually very easy to overwinter, and grow back well year after year. You can also take cuttings from them the winter to start new ones for next year.

Denninmi- Thanks for your response. I see you are in South East Michigan. So am I! :)