...turning back the clock to allow me to start at the beginning...
That would be a drive wipe. *Most* things uninstall cleanly, but not everything does. Fortunately, you don't always *need* to remove *all* traces; just enough so that a different version goes ahead and installs, and its setup makes sure that it runs like it's supposed to. There may still be traces of the old one, but the new one does work.
But if you really want to get rid of *all* traces, like if you don't trust the removal and reinstallation, then you're looking at a complete wipe and rebuild from scratch. Update immediately (that's going to take a while on a fresh install) and reboot, but don't change anything at all beyond what you absolutely have to, until the fundamentals work like you want. Then take a drive image of a working configuration (google how to use
dd
), so you have something to go back to if you break it again (same
dd
command, but with in and out swapped).
To make and restore that backup, shutdown and boot from the installation media again (usually a flash drive), and use the partition manager to see which drive is what. DO NOT MOUNT IT to see the contents! Or if you do or it happens automatically (it shouldn't), make sure to unmount it before taking the backup. Once you know the source (usually
/dev/sd_
), THEN plug in the big external drive that has enough free space on it to fit the entire drive that you're backing up, and a filesystem that can handle a single file that big. Mount that one, and have
dd
put the backup file on it. There are ways to compress that file as it runs, but those get to be hard to read on the command line. You can zip it later if needed, then expand it back to full-size before you restore.