Knock wood, I think I have all the glitches out of the setup of my main Mac. No rainbow cursor, and Time Machine is backing up the system. And I have a huge amount of space on my external boot disk. These were the main problems with my previous setup.
To get it done, it wasn't enough to get the new external drive set up, I also had to format the internal drive. And that was a little tricky, for me at least.
So I'm happy to have a radically nice desktop computer setup. Finally.
It should not have to be this hard...