you wrote "I would like the train to look right...." I hope it wouldn't sound offending but it was fun.
I wouldn't discuss the supply trains here, their length may vary but keep in mind usually they were even longer than the medical trains.
Now how the right medical train was looking.
The standard German medical train (Lazarettzug) consists of 37 cars 27 of which were "wards" and the rest 10 were offices, stores, living cars for the train and medical crews, kitchens, as well as one operations theatre and one apothecary, those 10 were evenly distributed between the ward cars.
To illustrate the things, here is a pic of one such standard German medical train belonging to Feldtransportabteilung Gruppe Ib, photographed in Maastricht area in 1940:
The ward cars were usually based on 4-axle passenger cars with average length of 15 - 20 m. The length of such car in 1/72 will be about 210 - 250 mm average. This means you'll need about 5 to 7 meters for those 27 cars alone, add a couple of meters for the locomotive and the rest 10 cars (which length may vary depending of the type) and you're in the picture.
I wish I had 10 meters to have a right looking medical train in 1/72...