I'm in the same boat as you- I have perhaps 12-16 feet by, oh, 1 foot for a layout in either HO or N. Either way, the new pike will be for switching, which will give me a chance to concentrate on building flats, kitbashing buildings, compressing-stretching out kits, etc. for potential shippers in HO, or whole structures for N. I have two prototypes in mind- the Frisco's Miami (OK) Branch, or the former MKT Sherman Branch from the ex-T&P main south about a mile and a half. The former involves a grain elevator, tire plant, steel works and plastics plant, while the latter has two grain elevators and a flour mill, plus uses for stubs of former Cotton Belt trackage. If I do the former, I have three GP7s to work with- if the latter, a couple of Geeps and one SW900 (the latter for the flour mill). And since the mainline runs is out of the picture (which is why it's called a switching layout in the first place), I can focus on switching cars. Plus, if I can cadge a little more space from the local BLM manager (read: the wife), I can include staging tracks on a yard segment that I can stow away when I'm finished running
Friscobob What you need first is: A 4-8-8-4 Big Boy to run on that Mainline, so it will look authentic!
Or I could model the one in the Age of Steam Museum in Dallas, first by slicing the rods off of the steam cylinders.......