For music and scoring work, because of just the thing you said with musical mode, tempo tracks, tempo changes etc., I never use a “master” project with the entire film for anything else than placing final stems and getting a “birds-eye” overview of the project. Each score cue in the film usually has its own project file, with the actual small chunk of film needed for that cue.
“Import tracks from project” is great for copying your current project’s “musical palette” to another project. You can choose to only import empty tracks, so that you really get a template but without the actual content from the other project. This should not make Nuendo crash, unless there is something actually wrong with the data you are trying to import…?
If you are working on several musical cues in one single project, you have to be careful. It’s so easy to forget to check every track version, every track’s settings so that nothing goes wrong. Making changes to the tempo track earlier in the timeline than the current part you’re working on, is a route to disaster. And changing time signatures earlier in the project especially makes things askew. So yes, dividing the film into smaller projects is what I’d recommend.
What I sometimes do when I want to use a lot of the same material or the same soundscape in different cues for a film, I do work on different cues in the same project, but not in film chronological order. I don’t insert the entire film on the video track, but only only the chunks I need for each actual cue. And if I add something new (like another cue or a new version), I add it to the end of the project. That way I can work on the same “mix” and the same orchestral palette if you will, without changing projects all the time. And use cycle markers to identify and export the different musical cues.
Hope this helps, sorry for the messy explanation, I’m fighting a deadline (while procrastinating, obviously!)