All good advice.
A couple more clearance thoughts...
1) While it's true that articulated locos will usually dictate the most problem on parallel curves with their swing to the outside of the curve, long wheel base cars...e.g., 21" passenger cars...will contribute to the problem with their overhang to the inside of a curve...especially the shaper curves common to O3R. Of course, when they're both traversing parallel curves, it's even more a recipe for disaster. Something to consider based on your own fleet and operating possibilities.
2) At this stage of your planning, it's not too soon to consider vertical clearance issues! I thought my several domed passenger cars would be the criteria. I even checked caboose cupola heights. Satisfied, I built the layout, placed tunnel portals, truss bridges, etc., etc.. Only to find that my assortment of RailKing double decker cars with die cast autos were way taller than anything else. Too late. Too bad. Sold them all.
FWIW...
KD
