I usually consider 5 couple a minimum for a regular contra dance, but
triples like Money Musk require more people.
A caller up here, Byron Ricker, has been writing a few dances that he
calls "quad beckets." Quad becket dances are becket dances that can be
danced with 4 or more couples and that never leaves anyone out (unless
there are an odd number of couples). Many, but not all becket dances
work this way. With just 4 couples left, I've sometimes called a quad
becket with some success.
Rich.