Hi Mark, just noticed these questions now.
1. I have no record of white being used, and early photos suggest a duller colour, so I suspect the beige is what was on the window frames.
2. Yes, those SSM wagons are fine, and the JM Design horse boxes likewise. JM Design also did a kit of a G3 2.4.0 - an iconic and ling-lived design, certainly appropriate to the era you have chosen (and many others!). Maybe John (JM) might comment as to whether this kit is still available?