Since we're talking numbers, the population of Blairgowrie in 2002 was just over 6,000. The power of Google!
As for Carlisles catchment area, Cumbria has a population of approx 450,000 whilst Dumfries & Galloway has a population of approx 148,000. Quite a large population , however for the majority of people there are already established airports and routes that are a lot closer to them than Carlisle (South Cumbria closer to LPL & MAN, North D&G closer to PIK & GLA).
I have no doubt that there is a market to be tapped in the North West England / South West Scotland area. However, I would question whether that market justifys a daily point to point service on a BAe146. The publicity that a failed route will attract could damage Carlisles chances of being exploited by the Lo-Cos in the way that Blackpool, Inverness, etc have been.