I'm using the resuscitated HD for CCC clones only (and maybe some other sort of data storage, since the free space is there). TM backup is now relegated to the replacement HD I got the minute [another exaggeration] the original tanked.
My computer guru assures me that the 3-way configuration leaves nothing to chance and is the way he's been doing HD-cloning with CCC for years. You are probably also right, but I'm going with his recommendations, if for no other reasons than he was able to resuscitate the backup HD and help me restore my Lion in 2013 when I had to have the iMac's internal HD replaced.
Your configuration is better than the one I suggested, because it keeps your backups on separate physical devices that aren't likely to tank simultaneously. (I thought you had only one external drive.)
Since you mentioned it, a note about Recovery HD... CCC lists all your mounted volumes, including connected externals, at the bottom of its sidebar, and selecting a volume shows you if it's got an operating system installed
and if it's got an associated Recovery HD; it also allows you to install a Recovery HD for any volume that hasn't got one.
