Along with his friend Allen McClelland and his Virginian & Ohio, Koester popularized the idea of proto-freelancing with his HO scale model railroad, the Allegheny Midland.
In 1966, with Glenn Pizer he co-founded the Nickel Plate Road Historical & Technical Society to preserve the memory of his favorite railroad.
In 1969, Koester and his wife and children moved from Indiana to northeastern New Jersey to take a position with Carstens Publications as editor of Railroad Model Craftsman.
In November 1985, he also began writing a monthly column called "Trains of Thought" in the pages of Model Railroader, published by Kalmbach.
In 2000, the Allegheny Midland was decommissioned, and construction began on a complex multi-deck version of the Nickel Plate's Third Subdivision of the St. Louis Division, also in HO scale.