My goal is to create a clean install of MacOS, yet still have access to the old install (somewhere else like another partition) while I work on the new install to match the old one. I am assuming that I will miss some items initially and will need to refer back to the older install.
One path to accomplish my goal would be to have a dual boot (though not preferred). While I am working on the clean install, I would be able to reboot to the older version to perform work if necessary UNTIL the new clean install is ready. Eventually I would delete the older version.
Another path could be to create a virtual box install of High Sierra, time machine back up that, while I work on making that right I would still have access to the old install (host). Then once I'm convinced that I have everything ready I would backup and restore the new virtual install as a real install on my Macbook.
Does anyone have any advice to accomplish this?