Dear Khun PPP,
I also suggest to change to LED, as they are more resistance in Digital and constant electrical current mode.
As for the directional lights, I believe that you will need to have 2 function decoders installed in the front and back wagons and put them on the same digital address.
Once the train moves in one direction one of the decoders will recognize that it moving to the front then it will display the white lights, the other decoder will feel that it is going backwards and put on the red lights.
This means that you would need to have 3 decoders ( 1 x motor decoder + 2 x function decoders ).
The easiest things would be to make the train set permanent and couple everything together and use only the motor decoder to run cables to both ends of the train to display the light correctly. This way you will save money, but the wiring is a little complicated.
As for the interior lights, there are ready made LED and also some with pick-up shoes for the wheel tracks.
Hope I was able to help.
Your Zug Haus Team