Thank you 6x6, but that still didn't fix the problem.
1) I Uploaded a file to iCloud with my phone. It shows on my iPad and in the browser, but not on my Mac. This shows that the issue isn't with the account, but with the Mac.
2) I tried to upload a file to iCloud via the Mac. It shows up in Finder on the Mac, with a "progress circle" next to it and a greyed out cloud, but not on my devices or on browser. That progress circle didn't move for more than 24 hours.
3) I deleted the CloudDocs file and restarted bird via Terminal as suggested on Stackexchange above. It looked for a while like it had solved it. I saw the "Setting up iCloud Drive" message for almost 24 hours, but it just stayed stuck there with a spinning gear wheel.
4) As suggested by some as a solution to unstuck the "setting up iCloud" process, I unchecked "iCloud" in the Finder preferences, shut down, restarted and re-checked iCloud. I'm back with the same list of sub-directories for apps I have never used (e.g.: automator, garage band, iMovies, etc.) but not the files I know exist on iCloud. That one file I uploaded via the Mac is there, with a "progress circle" next to it and a greyed out cloud.
iCloud still doesn't work on my Mac. Grrrrr