Hi, 8ntruck,
The NYC milk car is Standard O, (Scale Proportions), it's 11 &3/4" long, so your minimum curve can be no less than a 'O-31' diameter radius, not a 'O-27'--which would be a problem due to it's smaller diameter radius.
As, for the height it should be no problem, just measure from the top of the railhead, up to the bottom edge of an overhead object and the same with your milk car,( from the top of the railhead to the top edge, of the centerline, of the car's roofwalk.
When using confinement structures, such as tunnels, switches, bridges, etc.., not only is the length and height important, but also side clearence, so that each car of the train will be able to clear these surrounding obstructions, throughout the train's passage..
And, as for size of different cars being together, take a look of an actual freight and passenger train and you'll see the very same thing in real life, as in the model life.
Your, milk car, by the way, is beautiful.
Enjoy.
Take Care,
Ralph