We are all (nearly all, anyways) subject to buying locos and rolling stock that don't really fit a model railroad -- one each of all the big locos instaed of a fleet of medium sized ones. So my suggestion is to model one of the divisions near the major shops. Most railroads tested newly re-built or repaired locos on lesser trains on a line near the shops. This let them run-in at moderate speeds and loads for a couple of days. It meant that even crack passenger power might be pulling a branch freight or passenger train. So pick a lesser (but sturdy!) line running out of Altoona or wherever your shops were and let them run-in all the fancy locos you bought in a momentary brain seizure.