I really don't have a system for this, however in reflecting back, I've always purchased the locomotive first. For my most recent passenger train purchase ( only a month ago ) I first bought a MTH Premier baggage and coach set then separately I bought a RPO car all in Western Maryland Livery. They are pulled behind a H7 consolidation or a BL2 deisel both of which are WM locos. Although these engines are not prototypical for WM passenger trains ( K1 or K2 Pacifics and Hammerhead diesels ) they will have to suffice for now ... at least until I find a model of one of the WM prototype passenger locos.
For my N&W passenger train .... I first bought a Lionel scale J then purchased a set of Williams Pocahontas cars a year later. Additionally I bought a scale Weaver RPO, a scale Kline Coach and a scale K line baggage all in NW markings on the Bay one at a time.
B&O passenger trains ... I already had the locomotives before the cars. I bought two early MTH passenger cars on the Bay ... a scale RPO and a Diner ( my story goes that the diner has been converted to a snack bar/ coach ) Still looking for a real coach in B&O.
B&O trains are pulled by GP9, Atlantic, or a Hudson all in B&O livery.
Pennsy trains .... I bought the locos first again ...Williams scale GG1 powered and dummy.
The cars I bought a piece at a time at shows and on the Bay.... scale Williams and MTH.
My Pennsy Aerotain was purchased as an entire set new.
Reading trains .... Locomotive a FM Trainmaster purchased on the Bay followed 2 years later by a set of William scale passenger cars purchased at a show. They look great!
Im now looking to purchase a MA & PA scale passenger car. When the time is right I know it will show up.
