(1) Yikes, even though I copy/pasted it, I didn't realize you were saying Kbps instead of Mbps. The last time I had that was way, way back in Win 98. It wasn't nice, many sites took quite a while to render. But Outlook Express worked well, & there was no
OneDrive to deal with back then. I hope they will give you the full 758 kbps, but even that doesn't sound like much.
(2) Maybe turn on Files On-Demand at OneDrive's Settings tab...

Files you put onto OneDrive will still have to upload, but they won't download until you access them. Or, you can go to the site & access them there without downloading them, though that involves Kbps too. But remember, unless they are downloaded at the
time you make one, they won't be in a Windows system image backup either.
(3) I think it is File History that is responsible for your triplicates. Each time you make a change to file in the History, a new copy is put there. The old ones aren't deleted. You probably can exclude OneDrive from it. But do you really need multiple
copies, one for each change you make?
(4) I wasn't relishing a battle with permissions, so I'm glad it's over. And I'm glad you won.
(5) And I'm glad you've got backups of any files that went missing. I don't know what was up with that.
(6) Yep, some programs do become obsolete. Good that you've found replacements.
(7) Programs that have an option to uninstall should go quietly, but you are right they won't all do it. Then it is tedious & perilous to go after the remaining bits & pieces yourself.