Small town station positioning

Zandoz

FWIW, my few cents:

To answer your question:'How far should the leading edge of the structure (not the platform) sit back from the near rail of the track?'

I locate the front of my station building 10 feet (scale) back from the front  of the platform edge, not from the nearest rail.  If you DO want to measure from the rail itself, you will need to add an additional 2-3 (scale)feet to that measurement , to allow for the distance from the rail to the platform.

And to answer 'How common or uncommon would it be to have the diverging leg of a turnout to a near by siding passing through the station platform, just past the station/depot building?':

I would say, very uncommon, as most platforms tend to be continuous (one peice) units.  This is not to say it doesn't occur, but as platforms are essentially designed to allow passengers to have access to both the passenger cars and the station building, putting a spur at one end of a platform, across it and close to the building must necessarily limit train lengths and public (passenger) access to the train and platform/station; and as passengers a revenue source, to limit their access to either station or train is not good economic sense.

As I said, FWIW, I hope it  helps.

Komata

"TVR - serving the Northern Taranaki . . . "