I havn't tried it yet but a friend of mine sugested to me a good coat of bright yellow paint on rock castings as the first coat of paint.
His rational was that with all the sbsiquent coats of paint, dry brusing and washes that follow you can see the bright yellow and know you missed a bit.
On the industry try and choose one that has raw material coming in and finished product going out so a variety of wagons go in and come out and is something logical for the area modeled and have more than one if you have the space for it.
Don't forget the loco depot if you have one can also be classed as an industry for freight working with stores, fuel and sand coming in.
For repairs parts, scrap and empties going out.
All about the operational interest when it comes to play time