I haven’t said very much about this topic because I haven’t had much to add. I would ask you if you’re planning to use DCC or go conventional. Most of Bachmann’s On30 locomotive line has DCC, although many of Bachmann’s On30 2-6-0s don’t, particularly the ones sold as Hawthorne Village sets. If you do choose to go the DCC route, you may have to refit the HO diesel and steam donor mechanisms.
one thing I would definitely do is plan for clearances. Measuring the width of a borrowed On30 or On3 freight or passenger car is a good idea: even converted American Flyer S gauge cars are narrower than On30. Planning vertical clearances is also a good idea, especially for highway overpasses and tunnel portals. An NMRA On30 standards gauge is a good investment, but perhaps adding an inch or so of additional vertical clearance might be wise, even if you aren’t planning to run scratchbuilt D&RGW K-37 2-8-2s on your layout.
case in point: I belonged to a now-defunct South Texas On30 club and remember what happened when a member built a highway embankment and bridge as a view block for a scenery module. Bachmann’s 2-6-0 and out-of-production outside-frame 2-8-0 could duck under the bridge just fine, but Bachmann’s later 4-6-0 kept whacking the bridge. I hate to think what would have happened if those. 2-6-0s had aftermarket Colorado and Southern “bear trap” smokestacks. It would not have been pretty.
