We run King Air 200 and 350s from Gravel strips in the North. As long as you have guys who know how to drive on gravel surfaces we've had few issues with prop / engine damage (slightly more than purely operating on pavement, but negligible). One annoyance is breaks freezing up, with fresh snowfall and stinking cold. We have large screwdrivers to pry the pads apart, work fine, with some cold fingers. Also a few goofy gear indications in the extreme cold.
Perimeter (A company who fly out of Winnipeg) operate a fleet of metro's into some short gravel strips, and from what I hear do it well. I'm told it takes a skilled hand to pull this off and not scare your co-jo, or damage the props.
1900s are great for the longer strips, usually limited by ASD distances for many of the strips around the north.
The Hail Mary is still the DHC-6. If strips get soft, or a particularly short you can't go by this machine for STOL work. I hear the DHC-8 -100 is still a true de Havilland STOL machine, and most likely why it’s still used by a lot of operators north of 60.
Air North out of Whitehorse run a couple 737-200s with a gravel kit, and old Siddley Hawkers HS748s for their Gravel Ops. They are looking at swapping out the Hawkers for ATRs very soon. The fuel costs and Overhauls hassles for them engines are quickly making them in-efficient.
I think the legs you’d be looking at will be in the ballpark of 1000-1500miles. Enough to fly south to major centers regularly, but also enough to go north, and carry options for an alternate which are few and far between. As mentioned previously, most operators do a good mix of Pax and Freight, so some sort of “combi” is essential. Virtually everything is flown into the northern communities, so freight makes up a huge percentage of what’s regularly flown in.
If you had time it wouldn’t hurt to contact Calm Air or maybe First Air and ask what issues they have faced, and possible solutions they propose. Also
AVCANADA is a fairly active forum for Canadian Pilots and surely shed some more light for you.
All the best!