Most O-Scale vehicles are 1:43 scale (European O scale) but in my opinon that looks better with 1:48 scale O-gauge trains and layout structures, which I have. Your postwar locos and Plasticville are a bit smaller than 1:48 for the most part, and the advice given earlier to buy one of each scale 1:64, 1:50, 1:48, and 1:43 is good I think, to help you decide.
The vast majority of car models in O gauge sizes are made in 1:43 - probably 20 times as many as in 1:50 and 1:48 combined. Also really good models are made almost exclusively in this scale (I;m talking really exquisite models, like Brooklin and NEO that cost $75 - $225. But alot of big rig and bus models are made in 1:50 and 1:53, and will probably look good with you layout.
I wrote the book contained in the attached file several years ago, but nothing significant has changed, other than that a US-producer for operating O-Gauge wire-guided cars (similar to the European Faller Car System, but in either 1:48 or 1:43 scale rather than Faller's N or HO scale) now makes cars and roadtrack that works well. Anyway, this book might give you some ideas.