David, I am a zone 5 gardener in SW Indiana and I grow over 30 varieties of Hedychium and several other genera as well. I grow them all in 3 to 5 gallon pots. Mine overwinter in a cool greenhouse, down to 50 degrees, and we have weeks of overcast weather here in the winter, so not really a lot of light, either. Probably comparable winters to yours. Most all of my hedychiums bloom every year from early August on through the end of September when I have to start cleaning them up to come back inside. My plants don't really grow in the winter. They just maintain most of the old stems, though some of them tend to die back more than others.
First, congratulations on getting your H. coronarium to bloom indoors. You must be pretty attentive to your plants to do that. I find coronarium to be the easiest to bloom and one of the first to bloom each season, but blooming them in the house is always a challenge.
As far as your specific questions, do NOT unpot the rhizomes and dry out your hedychiums. They will likely survive, but you will set them back so much that you'll lose a month of growing season in the spring just to get them rehydrated and growing again. Keep them in the pots. If you can keep them growing fairly well, with adequate artificial or natural light, that's fine. If you want to cut them back to the pot and just keep them a bit moist all winter in a cooler area, that works, too, though they will be a bit slower to get going in the spring than ones that have retained some living shoots on them. Just don't put them in a warm and really poorly lighted area because the heat will push them to try to grow and they'll exhaust themselves without adequate light to make more food. If you have bloomed coronarium indoors, you probably have a handle on the right amount of light.
If you have further questions about varieties or care, you can post here or send me a treemail. I haven't been on this site much lately and wouldn't have seen your post, but another member (Deebie) told me you had a question about gingers. BTW - your Kahili (H. gardnerianum) is probably my favorite of all the ones I have. I first grew it in the mid 70's and I still love it today. Best of luck with your growing.
