Keep in mind that the type of locomotive you choose for your operations helps define your railroad and layout.
Most major railroads retired steam-type locomotives by the early 1950’s when they changed to diesel powered locomotives. You may find that steam-powered era themes include windmills, classic vehicles, no high-rise buildings, etc. Therefore, you may have a broader range of theme options with diesel powered locomotives that were broadly introduced by the major railroads beginning in the 1940’s.
As you consider the type of locomotive you plan to run on your track, you may want to consider its actual size in proportion to a life-size one. Its actual scale is dependent on how much space you have allocated to your railroad. Popular sizes scales are 1:32, 1:29, 1:24, 1:22.5, and 1:20.3. If you plan to include a bridge or a tunnel, make sure that your locomotive, tender, and other rolling stock will have enough clearance to go through.
This is an example of a freight train you may see in your vicinity. In the railroading industry you will find all sorts of specialty cars that can make your particular railroad unique. Flatcars with cranes, tankers, gondolas, coal cars, boxcars, refrigerator cars, etc. make a train interesting. However, as a reminder, you need to keep in mind the era you are working with.
Diesel passenger trains don’t have freight cars as part of their trains. Due to changes in technology, you will no longer see a caboose at the end of a freight train; however, you will see one on this freight train, primarily because it looks good on my railroad.
As you gain more experience, you may want to add a siding for your switching operations that may include an auto reverse feature. A trolley operation also looks good as it goes back and forth on the line. The following video is Phase II of the siding project. Phase I was building the siding and Phase II was setting up a functional auto reverse operation.