Ok, I think I have my answer. Regarding Final Cut, you can assemble multiple timelines (sequences) inside just one project. For longer form work, this is nice as it keeps the timeline less complicated. You can work on sections of a project one at a time and then assemble them into a project timeline (sequence).
After all that, you can then open MULTIPLE projects at the same time, while copy/pasting or nesting the master sequences into a final assembly timeline. sort of like nesting a nest but it works.