Fear an Ignorant Man more than a Lion- Turkish proverb
Modeling an ficticious HO scale intergrated Scrap Yard & Steel Mill Melt Shop.
Southland Industrial Railway or S.I.R for short. Enterchanging with Norfolk Southern.
You've gotten some excellent advice so far! Let me see if I can offer something to go with it.
You have an idea of what you want, and that's a good place to start, but it'll need a little more focus. As already stated, yards take up a lot of room. Thats not something you're blessed with. You might be able get that yard but limit it to something more in keeping with your size constraints by modeling a large industry. This way you get a small yard and a connection to the outside world in a more compact package. The physical plant or industry would be large, and the focus of the layout, but you could later incorporate it into a larger plan and you'd already have a major player up and running on the new layout in no time.
Industries you might concider would be a small seaport, a paper factory, a steel mill, an animal feed factory (like Purina), an auto parts manufacturer (like say, tires), or somethng along those lines. Stay away from industries that cover a lot of ground like a fireworks factory, a refinery, or a munitions dump. You don't have the room to make them look right.
The right track software from Atlas works pretty well and it's pretty easy to learn. You just have to use it some and you'll get the hang of it. It has N scale track (both code 80 & 55), but only the Atlas brand. Here's a link; http://www.atlasrr.com/righttrack.htm . Some people prefer Xtrkcad. It is more powerful and offers all kinds of brands of track, but it also takes a bit more to learn it. Do the tutorial and then play with it and you'll do OK. Here's a link to it; http://www.sillub.com/ . Both of these are free programs.
Design software is only one step though. You need a clue as to what you're doing with the software if you want a successful design. Read through some of the stuff on this site ( http://www.vetmed.auburn.edu/~smithbf/BFSpages/LDSIGprimer/TOC.html ), especially the stuff on yard design, and you'll have a good idea of what things should look like to operate correctly.
And always remember, ask questions! The only dumb question is the one you didn't ask!