12 passengers on a 2000 is a bit of a squeeze… I think it looks tight with 10 pax config, so shoving in another 2 seats somewhere is going to be tight.
Although, if you are only planning on 1H15 - 1H30 flights, not too much of an issue. I have never seen a 2000 with a 12 seat interior, so that may have to be something that is done post purchase by a completions company.
Also, is the 3 crew essential for such short trips?