As for the use of a flat pick between thumb and index finger then use the middle and ring fingers for a three-finger style finger picking pattern, didn't John (I Wish I'd Landed In Grandma's Feather Bed) Denver do that, and on a 12 string to boot?

I use thumb, index, middle and ring (classical fingering), which allows me to do some wild variations on clawhammer.

Never tried the Zither, but I do play the '3rd Man' theme complete with harmonics on the guitar...