For me, part of the fascination with this scale of railroading is building these miniature trains in the same manner as their full size, main line brethren.
Excellent - an excuse to discuss diesel-electric locomotives!
For those who are not into trains, a typical diesel-electric locomotive has a diesel engine driving a generator, which connects to the drive motors; there is no battery, and the electrical system acts as a continuously variable transmission which can run with an infinite reduction ratio. Traditional diesel-electric powertrains in heavy off-highway dump trucks and boats and ships are similar. Generator and motor types and the control system between them have changed of course over the decades, because diesel-electric propulsion started long before high-power electronics.
The diesel-fired generator set and fuel tanks can be replaced with any other electrical energy source and the drive motors (and their installation) can stay the same - this makes turbine-electric, hybrid diesel-electric (with battery), hybrid diesel-electric (with third-rail or overhead wire electrification), pure battery-electric, and fuel cell hybrid locomotives easy to build... and all of them are out there on the rails.
The inherent characteristics of the direct diesel to electric system are largely easily duplicated with a battery, controller, and any motor... if the controller has a current limit (corresponding to the current limit of a diesel-electric and establishing a low-speed drive force limit) and a power limit (corresponding to the engine power limit of a diesel-electric) that applies regardless of speed. The battery voltage directly corresponds to the voltage limit of a diesel-electric system. The current limit has to be low enough to protect the battery, the controller, the motor, and the train structure (how hard can you yank on that first passenger car?); it also should be low enough to avoid spinning the drive wheels in normal conditions. The part that needs some thought is how to interpret the "throttle" control: the usual train practice is to use it as a power request, but at low speed that makes it too sensitive; the normal approach for an EV is for the "throttle" to control the current (and therefore the torque), but in the train that means that as the train speeds up it will use more power, not like the real diesel-electric locomotive. Current control is likely the reasonable way to go.
My understanding is that the motors of diesel-electric locomotives (and electrically driven cars of trains without locomotives) are typically mounted directly on the trucks (so they turn with the trucks, and are not supported by the locomotive or car structure), and there is one motor per axle. That would certainly work in scale, although with a chain drive it is reasonable to drive both axles of a two-axle truck with one motor.
A diesel-electric locomotive normally has dynamic braking, which means running the motors as generators and just discarding the generated power through huge resistor banks. In a battery-electric system the equivalent is regenerative braking: again the motors are run as generators, but the generated power recharges the battery. Series-wound brushed motors are not capable of controlled regeneration or any other form of generator operation unless the field (stator) winding is electrically separated from the armature (rotor) winding and suitably controlled. What's the plan for braking? Unlike a diesel-electric locomotive, scale gas or diesel engine-driven locomotives presumably wouldn't use braking by the drive system, and I suppose they can just use the brakes of the cars being pulled. I remember the power lever on the train that I drove, but I don't remember what it had for brakes.