So first thing to consider is the site (and so ultimately the size) of the layout. My Model railway room is 10'6" x 9' 6" and houses "Purespring Watercress", my Gn15 layout. "Gonou", my T scale model. My "Underground Armaments Store" 1:32n2 layout and "Oneota Yard" my Ho American layout. The room is in dire need of a cleaning and tidying as my wife often points out with remarks like.
"I can tell you've tidied up. I can see the carpet"
Despite that I have calculated that with the layout mounted at 50" off the ground I will have the full length of 10'6" available to me. Looking at shelf width I think 16" is quite reasonable. So there we have the maximum layout size 10'6" x 16".
My ego always wants to show my layouts off so I should plan this to be an exhibition layout. Lightweight construction methods will rule the roost.
As for the prototype for the model. There is no doubt in my mind that it has to be an East Lincolnshire Branch Line. My family is 9 generations of Lincolnshire Yellowbellies. I still think of Lincolnshire as "home" though living in America.
I've been pondering Lincolnshire based model railways for as long as I've been modelling railways. So it really is a no brainer.
The years the I remember would be the late 60's and early 70's which would mean that locomotives would be predominantly Green with a bit of BR Blue sneaking in.
So to recap, the plan is now to construct a model railway layout, maximum size 10"6" x 16" of an ex- Great Northern Railway East Lincolnshire Branch Line in the late 1960's - early 1970's.
That's a good start to go on.