Ok, night night. Maybe if it's all encompassing, I won't have anymore questions after that. Yeah, right. A person can dream.
Actually, I looked out my window, and then at wunderground.com, and I realized that yesterday was the first Coney Island Boardwalk day of the season, and then I found out that Angel, my beer guy who generally has only Coors Light, which I find undrinkable, also has vodka & OJ, and the rest is unfortunate history. Alcohol and bright sunshine have always done me in. But it WAS worth it!
1. Now that Macintosh HD has been repaired from Recovery and we've determined that your external hasn't got any bad blocks you're ready to proceed.
2. I'd delete all extraneous partitions from your internal and leave only Macintosh HD, i.e. "Sierra." Caveat: If you decide you'd like to maintain an onboard clone you'll need a second partition, which will really only be feasible with a second APFS container.
3. I"d wipe your external, reformat it HFS+, and partition it with five x 100 GB partitions and one x 500 GB partition. APFS is and will remain meaningless on that drive, because you've got only 44 GB of OS and data combined, and 1,000 GB of space, i.e. you'll never run out of space unless your computing habits change VERY DRASTICALLY. The five x 100s will give you ample space for backups of Sierra, High Sierra, Mojave, Catalina, and whatever comes next, with the 500 GB partition leaving you room for whatever unanticipated extreme need may arise.
4. As far as cleaning house goes, I suggest that you do it before upgrading so you won't have to clean both "XYZ" and Sierra on your external afterwards.
5. Next, I'd clone your house-cleaned Macintosh HD to your external...which partition isn't particularly consequential.
6. Now, choose your poison, i.e. High Sierra, Mojave, or Catalina, and
d/l it while booted into Macintosh HD on your INTERNAL drive. The installer will go to /Apps.
7. Launch and run the installer. It will overwrite Sierra to "XYZ" but leave ALL your apps and data intact. The same scenario applies to running ANY upgrade over ANY previous version (except for the Catalina possibility of a folder on your desktop mentioned by joemike, and like him I've never found anything in one of them that meant anything to me or affected my computing).
8. If you choose to upgrade via a "clean install," you can run Migration Assistant to import your apps, data, and settings from any other volume.
9. 32 v 64 bit apps: Even if you upgrade to Catalina, don't give them a second thought UNLESS, like some FTM posters, you're running one or more apps that you absolutely can't live without or are too expensive to update/grade, Adobe CS being a prime example.Yeah, it would be nice to be able to maintain all your inconsequential but beloved apps, but the cost of being unable to upgrade makes it a losing option.(I lost a couple myself, but nonetheless, I've never looked back.)
10. Learning curve #1: I upgraded from Snow Leopard to El Capitan, a jump of four OSs, and didn't run into any problems. The first thing I always do after any upgrade is go through System Prefs to see what Apple has jackassed around from version to version, and I let features resolve themselves. I don't recall ever losing any important ones; my real problem has always been uncovering the new ones.
11. Learning curve #2: I don't remember in which OS versions or order they phase in, but you WILL run into some new security features as you meander along the upgrade trail, but in each instance they're presented in the form of (generally
) intuitive pop-ups accompanied by expert interpretation here at FTM.
12. As has been previously mentioned, Mojave will give you an HFS+/APFS option (Take APFS!), and Catalina will auto-upgrade to APFS, but all that is so far under the hood that you needn't worry about it. (It's pertinent to me because I"ve always been a big-time partitioner, and to joemike because with APFS he's become one.)
Ironically, the biggest learning curve item hasn't been mentioned yet... Safari 12 will "kill" ALL your extensions and necessitate their being replaced with apps, either from the App Store or freestanding, that may or may not replace your lost functionality. You're going to be on your own in that respect, although if you tell us which ones you're running we may be able to help.
If you upgrade only to High Sierra, though, there's a saver: The d/l to which I linked you installs Safari 11 and perpetuates your extensions, but (CAVEAT) if you allow Software Update to do its thing it will update Safari to v 13 and undo the saver.
Well, that's my take on things after taking into account all I know of your computing habits, all the excellent info provided by the other posters to this thread, joemike in particular, and all I know and can think of.
I think, read hope, I've touched all bases without getting too technical.
