What type of track are you proposing? Ohio is fairly moist, so aluminum would be a nightmare to maintain. Brass would require a full 1st Division, just to keep functional, with daily cleanings.
That leaves stainless steel, or nickel silver, both on the spendy side. Fortunately, it’s a one time expense.
As to types of plants, your local nurseryman would be a better source, he knows the climate, and what will thrive. Alberta spruce are ubiquitous in garden railroads, though. They can grow to 7 ft, if left alone, and trimmed to represent a giant Sequoia, or Redwood. 6 or 7 ft, times the scale of your RR is a 140 ft tree, which is how tall they get. Usually, they are kept in the 4-5 ft range, but imagine the possibilities. Once established, they are difficult to kill by trimming, but they will die overnight for no known reason. Start the trimming before planting, it’s easier that way, then once, perhaps twice a year to maintain.
Various dwarf cyprus are a possibility, as are dwarf maple. Irish moss and Scotch moss make good grass substitutes. Sedums and thyme are good fillers. You might consider an herb garden for SWMBO.
The possibilities are endless.
