I did have some success with planes as small as ERJ135s, or even SW3, but I usually respect the turnaround time. A SW3 can fly 6 times during the day(or 5 in the day and one in the night), if it has short routes to serve. Even with the secure 25 minutes turnaround.
2-3 planes per base is not viable, but 10-12 can work, though I prefer hundreds. In Visby, I had just one E190 and 12 SW3. You do'nt make much money with that, but you make some.