Well, here is my submission. SCARM file is attached. Being you asked for dual scale, one being tinplate, and wanting operating accessories, I went with a simple toy layout. Something that can be nice to look at, but also fun to operate.
I couldn't find any Standard gauge track in SCRAM, so I just used Atlas O for all of it. The Green is for the Standard gauge and the rest is O. The tan blob at top is a mountain up against the wall. There is a passing siding on each gauge in the mountain. This allows you to do some nice visual "trickery" by having two trains on each loop. I believe Dale H of these forums has posted info that allows you to have train B sitting on the siding while Train A is on the loop. As Train A enters the tunnel it goes on the free leg and stops short of the switch. Now Train B leaves and travels the loop, and once it returns to it's starting location it stops and Train A takes off. You could have them pointed the same way so one goes in and a different goes out. Or I'd rather point them different directions so that after one train goes in and disappears, the 2nd comes out the same side! The O gauge is set up with like manner, only there is a spur that comes out of the mountain into the middle and splits. Here you can do logs in one spur and have the saw mill put out planks the other side. Or you could have a hopper dump on one side and another gets filled on the other. Or you could have a crane move items from one freight car to another. On the bottom is another siding with a place for two operating accessories or industries. There is also a spur that goes off to another place. The blue squares are the operating accessories or industries. Pink squares are downtown like buildings. I know MTH makes several. The green squares are houses, again with ones like MTH makes in mind. The gray is road for cars to be placed on. As for getting to the track in the mountain, I'd make it either open benchwork in the mountain so you can get to it from under it, or make the mountain lift off and the table strong enough to stand on, and walk along the road to get to what you need to. Nothing is to scale.