How Do I Convert Old Media Files Before the Upcoming macOS Update?

I have many hours of old iMovies (made from 8mm and Digital tapes), iDVD, FCP and others apps. I just read this article: “Apple is killing QuickTime 7 in macOS 10.15: convert old media now” by Eclectic Light Company 3/23/2019, and it advises to “convert old media now”.
I have an old Sony Digital8 player (FireWire output) and an iMac (27″, late 2013) running Mojave. I have iMove 10.1.11 and FCP 10.4.6. Due to hard drive malfunctions in the past, i’ve lost many of the files that were converted, so, i have to start over on most of the material.
Any and all recommendations would be greatly appreciated on the specifics on how to get this done. For example, there are many video start stops on a single D8 cassette: Do i run iMove/FCP and “let it run” to end up with the many individual files?
However, some files do exist. How would those be handled?
If not completly answerable here in the Forum, maybe the focus of a future macmost video? Thank you so much for all you do!
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Rick Apodaca