I found this tutorial on creating a low poly aircraft model that looks promising:
https://www.fsdeveloper.com/forum/threads/blender-creating-a-low-polygon-airplane-tutorial-bij-karan-shah.440892/Think I'll get the building (parking garage) in place without the B-25, then terminals and jetways, then add the plane another day, once I figure it out.
If it makes any difference to your recommended approach to this, I looked again this morning and the .ac file is 4.8 MB, much more reasonable. I don't know what I was looking at yesterday.
Might do one of the other planes first, as they may be easier to do. Then again, FG low poly models may already exist for them, I haven't looked yet.
Thank you , CaptB and Gooneybird, for your advice.