circuit breaker for post war ZW

Breakers are a great idea.  There are people on this forum who will describe the ideal ones for you. I would also suggest TVS diodes for each of the outputs, as well.  Those diodes protect agains transient high voltage "spikes" which circuit breakers do NOT protect against, but which can damage the electronics in your locomotives.  Any time you see sparks in a situation like a derailment, for example, spikes are being produced that can cause the damage to electronics.  Even having a circuit breaker trip while there's a load on the circuit can cause the same kinds of spikes. Having both forms of protection is the way to go.

I use a 10 amp magnetic circuit breaker on each of the throttle outputs ( A, B, C, & D) and a 15 amp magnetic breaker on the U terminal. I also use TVS protection, but at the track.  I use them on illuminated lock ons, the light bulb also helps suppress voltage spikes. If your are running modern electrtronic locos, it would be good to not connect accessories with coils, like switches and uncoupling tracks, to the same power you use to run your trains.