Nick,
The Avistar is a good flying plane, I put an ARF version together a couple of years ago for a friend and it fly fine. I was able to train him fairly easy. But my personal opinion the SIG LT-40 (kit or ARF) is the best trainer out there. I have had trainees solo quicker on the LT-40 than any other trainer. It is so forgiving and stable, especially in turns. The only thing I would suggest if you get one is to replace the Elevator and Rudder pushrods that come in the kit. They have a tendency to expand and constrict drastically with the change in temperature.

As for your question on the flight simulator. I have been using the PT40 to train people during the winter months. It seems to fly realistically. Just remember when you fly on the computer you don't get the peripheral and ground reference as you would at the field.