I line of which I'm very fond, and Killin junction in particular, and one I have visited on many occasions. I have drawn a plan in AnyRail, in N gauge (and for Callander for that matter), so the pointwork doesn't flow as well as handbuilt track will, but all the same it's a great location for full length trains.
Is there going to be a partition/backscene between the station and the vaiduct?
Backtrack (the magazine) had a feature on KJ a couple of months back with nice images of part of the buildings, etc. If it will be of interest I can scan and send it to you if you like.
Best
Scott