Forgive me for this question, but I am totaly new to the hobby and just learning as much as I can. If I am modeling the Cascade moutains in the modern era and have a lumber mill, a mine, a feed mill, a freight house, cold storage, oil depot and a grain elevator, what sort of rolling stock should I acquire? And do they have to match the railway locomotives?
Your rolling stock can include pretty much any modern car out there. From modern log cars to centerbeam flatcars, to boxcarsand chipcars. As far as matching your locomotives, I grew up in the area you are planning to model. even thought about 75% of the rolling stock may be from the home railroad, there are enough cars from other railroads to make things interesting for you. Have fun with your railroad.
I assume by "modern" you mean, say, the last ten years...here are a few suggestions, by no means exhaustive. You mentioned: a lumber mill: Red Caboose has made some very good centerbeam cars. a mine: A coal mine? Kato, Athearn, and Deluxe innovations have all made modern aluminum coalporters a feed mill: see below a freight house: for a modern layout, you want boxcars without roofwalks. Intermountain, Fox Valley Models, Athearn, and Atlas all have put stuff out there. cold storage: hmmm...here's a gap someone could fill. I believe the most modern looking reefer was done by MDC quite a while ago, and the paint schemes are suited to the 80s. They are good cars though. oil depot: Try Atlas 25,500 gal tank cars. Don't get paint schemes for food companies like ADM though. and a grain elevator: Intermountain released some very good Trinity hoppers. And do they have to match the railway locomotives? Nope.
Not to mention Geeps & SD units for switching depending on railroad. BNSF is using SD40-2's for switching. But if you looking for rolling stock check in here N Scale (Purchase It Now) - TrainStore for some good deals.
I am in the process of liquidating my late friend Steve Dobbins n scale equipment. I have several of the Red Caboose centerbeam cars and loads if you are interested. I also have the Walthers Feed Mill still in the box. Jeff
If you are doing wood products in the Pacific Northwest, you'll want some woodchip cars, too. Deluxe Innovations has made several excellent ones in the past several years. Currently, I think they've got a re-issue of BN ones out. I still see these often. If you do logs, too, there's an N scale kit outfit (used to be Alan Curtis, now it is someone else... I will see if I can find a URL) that makes kits for making log bunks such as are still used quite often around here.