Glad to be of assistance Matt.
RE dry brushing - I like to use ~1/2" wide flat tip brush when applying paint to the large surfaces (i.e. car body sides, ends and roof). As a reminder - the roof walk and roof walk saddles were never painted (for safety reasons).
For unpainted areas such as the car underframe, roof walk and saddles, I prefer to use a diluted solution of black India ink and denatured alcohol (90%). This gives a nice ‘weathered’ wood appearance. Some folks like to use liquid black shoe polish and alcohol, but my experience is that it left the wood shiny.
RE applying bluing - be careful applying bluing to in place parts. If the bluing gets on the surrounding wood, it is not going to obsorb paint as well. I have never tried painting the car and then bluing the parts - it might work.
It is very refreshing to see a young adult showing interest in model railroading, much less garden railroading. I for one, will support you 100% all of the time. YOU are the future of garden railroading!
Jerry