Illia

Storing them at anything non-freezing but below 55 degrees is fine. Cutting back that much is fine, but also remember that they can be leaned against the wall which helps save on height. Another thing, by the time they're 8-10 feet they should be able to flower in a season. But, this is where dwarf types always come in handy. Cutting back a banana is perfectly fine but don't cut them at too tall or too late an age, as you might cut the flower bud inside.

So, if you want to cut, don't do it too late. Your first year you should be fine, it's the next year that you'll really start asking questions. In a year, a standard 10+ foot variety will grow, at least out here, a max 7 feet at the P-Stem. It's still got a lot left especially in terms of time, so no cutting is needed. But, if it were, it's still early enough that it would be okay. Once you put it out the second year, it will continue to grow taller and that's when you start asking questions about the next winter, unless of course it is an earlier blooming variety.