Required addons:

Freeware:
https://rail-sim.de/forum/filebase/entry/976-kkt-waggon-repaints-v-1/
https://rail-sim.de/forum/filebase/entry/974-kesselwagen-repaints-v-1/    
(repaints)

Payware:
https://trainteam.berlin/forum/index.php?/topic/1412-br151-pluspack-details-und-bestellung/
OR
https://trainteam.berlin/forum/index.php?/topic/1394-br143-pluspack-details-bestellung/
(sounds)

Installation:

As easy as it can be. Just grab the "Assets" folder from this zip archive into your Railworks folder and overwrite the files.
"C: or D: (or on whichever disk you have your RW installed on)\Steam\steamapps\common\RailWorks"

And that should be it. :)