Boslandew:
You would go bankrupt trying to operate a Dash 7 on that route. Sure, the PLANE could do the job for you perfectly, but the maintenance costs for a four-engine aircraft of that size (not to mention the fuel costs) would kill the idea at the planning stage.
Best suggestion I can offer, if you need to carry more than 19 passengers, is to get TWO Twin Otters. No-one will ever complain about increased frequency of operation.