I see only a disadvantage in using stereo heads - it would reduce the recorded area on the drum due to the gap between the two gaps on a stereo head. The two gaps are one above the other.
As far as how many heads to use, you will need one playback head per echo repeat. As Dave said for those of us trying to duplicate Hank's early echoes that will mean a minimum of four playback heads (plus of course the record head).


