That's a good point. I spared them because they are no props and for this they consume more fuel. They are also (much) larger and can fly longer distances, but business class also could be build in the three props I named (ATR not for sure 100%, just 99%).
To your questions; theoretically you can fly the F27 till 2030, but remind aircraft must be scrapped after 35 years or so (I don't know this exactly, but I think DanDantes knows, he's based at Chicago in DotM #2).
The Saab2000 is a good aircraft. Good speed but high fuel consumption (compared to other props of this time). If you take it's release date ~1993, you could also go for Fokker 50 (much slower but higher range - 1030nm vs. 820nm and 240kts vs. 352kts), DHC-8-300 (released 1989 in basic version), ATR-72 (same fleetgroup as ATR-42, released 1991) or smaller jets like Fokker 70 (same fleetgroup as Fokker 100 which is released 1987).
You see, there are many many possibilites.
If I were you I'd stick to F27 and later change to BAe ATP and if this is too big, just put standard seating in it.
To replace the BAC-1-11 I would maybe - if I have enough money - use BAe 146 and later change to Fokker 100 (1987) and Fokker 70 (1993).
However, I don't know exactly the demands of Belfast, but this should be ok for you. At the end it's your decision and you can't do anything wrong with every prop. They will always make decent money if you have a bunch of them and something bigger to support. Just make sure your aircraft has more than 40 seats (better 50).
And don't go after the CRJ100/200