Thanks again, everyone.
To answer the questions:
Steve, the paint on the ballast car was fairly simple. I sprayed the frame (it's actually white metal) with Floquil Earth. After that dried, I semi-drybrushed it and the ballast gon with Apple Barrel's "Indian Red" acrylic craft paint. (I use a lot of Apple Barrel/Plaid/Ceramcoat/Americana craft paints; they're easy to find and very inexpensive!) Finally, I
lightly dusted the whole car with raw umber and gold ochre chalks.
As for the weathering on the trucks, this is also a simple process. I pour approximately 1/8" of alcohol in a small jar. Then I scrape two or three different rust-colored chalk sticks into the alcohol until I have a nice rusty "slurry." Using a soft, round brush, I paint the slurry on the trucks and springs (also the coupler heads). If it looks too heavy after it has dried, I use a stiff bristled brush to remove as much as necessary.
I also use the slurry mix to "rust" rivets, nail heads, corrugated roofing, etc. It's quick and easy.