If you haven't already, check out and join the International Bananas Society:
http://www.bananas.org/
There's a wealth of info, including forums devoted to cold-climate banana growing, overwintering, best varieties for cold climates, etc. It's a very welcoming and useful site that many banana growers belong to - tropical to sub-arctic, breeders to amateurs.
You may very well find answers to a lot of your questions just perusing the forums.
