Thanks for everyone’s help!
I finally found the culprit.
Freeze frames.
I opened last version I could open (before any changes were made yesterday), started over, and saved after every couple of changes (a real pain!). Very early on I had a still frame from some video. When created using “Make Freeze Frame”, the project crashes on open at 40%. When exported via “QuickTime Conversion” as a still and then imported, the project opens fine.
Somehow the “Make Freeze Frame” frame is corrupting the project file itself (why else would it crash without any media?)… And then the problem only becomes apparent after you quit FCP and then try to open the affected project file.
Weird….
Aaron