How to install lighting in scratchbuilt wooden op coaches.

FWIW, I would switch the trucks to the MTH Old time wood trucks . Get rid of the bolster under the coaches and you have your power pick-ups.

Unless you are 2 rail, new trucks with roller pickups are likely easiest and best.

Going to metal wheels would make common easy. Otherwise you need to make "whiskers" to rub the rail. Solid wire works pretty good for this.  Small gauges make thier own often. (I have one O example, but it might take a day or two to post a pic).

I've made center shoe pickups out of automotive brass feeler gauges wrapped around plastic tubes with the axles simply passed through the plastic tubes.

More drag than a roller but actually makes for a great pickup with less flicker.

This is a fantasy piece. The wheels (just 2) are S gauge plastic in an O truck. The white wire is solid and just hangs stiffly, rubbing the rail.  Better placement and angle allows it to manage across switches. You can't put in less effort to hide it ..(a tri-pod, the center pick up is the tack.)

It does a better job than you might expect, but a diode and cap can smooth out things as well.

If messing with custom sliding shoes, wipers, contacts, whatever gets out of hand, how about battery power?  If you're considering LED lighting, USB battery-banks based on Lithium cells are remarkably small and could power several passenger cars for multiple operating sessions.  Charge via same micro-USB cable as your phone.  One idea could be to hide one battery bank in one car - if it can be suitable hidden - then run a 2-wire tether between cars carrying 5V DC.  Then use 5V LED strips.