Upload & Sell: Off
I would suggest (at minimum) a work drive (preferably SSD) and a "data" drive internally. Current work should be on the SSD and regularly copied to the data drive. (I copy updated catalogs and RAWs to the data drive every time I close LR)
Then, I would also suggest (again, at minimum) a third "external" drive (USB3, TB, whatever) that is a clone of your "data" drive. I would regularly (your choice of how often) "echo" the data drive to the external, and keep the external in a fireproof safe on premises.
Once you have all that in place, create a 4th external that is a clone of the data/3rd, and keep it in completely different location. (bank vault) Swap the 3rd & 4th out on a regular schedule. (weekly at minimum)
This is pretty much what I do. It's probably the most basic plan that simply works.
Like joosay, I plan to setup an "online" backup at some point that will echo my "data" drive constantly.