I agree with Hypno Toad, your feature list seems pretty reasonable. I'm in SW Ontario for reference. I'm not sure I'd include thru-axles as a must have.
I've done singlespeed, and while it was serviceable I prefer IGH. I like having higher gearing for clear days and lower gearing to churn through snow drifts when necessary. My dislike of freewheeling downhills may be unreasonable.
You could consider any frame with semi-horizontal forward-facing dropouts. A threadless headset would be ideal but not necessary - makes finding bars/stems easier. To winterize, build up a wheelset with drum or roller brakes and IGH, which is what I've done to improve the all-weather performance of my non-disc Surly LHT. Make the front a dyno-hub for bonus points.