The trick I found to getting a secure Sergent Engineering scale coupler in P-B-L equipment is to add a 2.5mm O.D. styrene sleeve around the coupler screw to secure the coupler and allow a little play. I had to ream out the Evergreen styrene stock a bit to get it to fit, but has a great action now.
From 1900-1950 is a Halcyon period of steam engines, a variety of operations, shortlines, narrow gauge, passenger operations.
Do you like brown boxcars? Do you hate Helvetica and anything jet set? Do reliable diesels seem too easy to you? Do you like squinting at silver nitrate negatives to try and discern what color to paint something?
Those good old days when you had plenty of time to watch trains and no money to buy them.
Does it give you a concept you can work what you want into? Are you in the demographic that manufacturers are catering too?
It is what you are appreciating now. You can go take a nice color photograph of it, or better yet, someone else already has and posted it on the internet.
Limited switching and shortlines. Most trains 3+ engines and 100+ cars, difficult to model on a modest layout. Really easy to just spend your way into a layout.
Easy to get materials
In your basement is the same as outside.
Tropical port / city? Icy Alaskan tundra? South American mountainside?
May look nice, but have limited operation potential, and be harder to get accurate detailing of.
Exactly what you want
May be hard to keep coherence when you keep piling things on.
Early attempts at a tool to show era-specific information to help modelers define a scene. Many times a modeler wants to incorporate elements (era, location, line, equipment) particular to their own tastes. You could narrow down to a month, like Jack Burgess' Yosemite Valley in August, 1939, or pick a whole decade to model. There is no right answer, but many exciting options.