OK, last night I bought and added two 1TB drives to use as a cache pool. Adding them went without a hitch. Once all were formatted, I clicked on the first cache drive, and I hit the button labeled "Balance".
I then restored everything I had from my cache drive backup (the appdata folder, and a VM). Made sure that appdata share was "cache only". Finally I recreated my dockers (saving the docker image in cache drive) and all is working nicely.
I clicked the first cache drive again, and I notice the below:
Do I need to hit "Balance" again? How often does one need to "balance"?
Many thanks for all the advice.
H.