Spillage is critical ON the layout?

Hmm...never thought of it that way, but I have always been a kinda sloppy scenery guy. Finicky with the finished result, but sorta all-over at the plaster/rocks stage. I guess I just figured it would be ground-covered over and the track was protected by tape already.
Nice work, Biased Turkey. Yes, please, show us more as it progresses!
Check out the wild variety of ground coloring that John Allen used, (and the way it all seemed to change depending on the lighting effect for the various shots. Of course, that varied according to rock strata, etc. but also for just the ground. Still, it was mostly tan...
I have to admit I was/am a tan base coat guy. But my tan is actually more of a red clay color commonly found in Appalachia. There's something nice about layouts with a unified base coat that permeates all the weathering, rocks, ground cover, etc. The layouts that, to my mind, have a polished, 'pro' look seem to demonstrate this. I think it's a limited variety (not a "one of every bag off the rotating WS LHS display" mish mash) technique, and it's trying to emulate a prototype. Even some freelancers pull this off.
Frary, in his scenery bible, advocates putting drops of your base coat in a mister (highly diluted) and just misting the whole layout - buildings, trees, roads, ALL, to blend that base coat in and unify the scenery. Not sure I'd go that far, but it bears consideration.