For many years a man named Jim Hicks has run not quite monthly dances in the Peoria IL
area. He certainly once faced the same challenges you now face. Their Facebook page
is
https://www.facebook.com/rusty.pickup.barn.dance/
You might want to contact him through his FB page about his experiences and advice.
Plan your dances (which I speculate last 2 or 3 hours) so that the earlier dances teach
the figures used in more interesting dances near the end of the session (by which time
some of the newer dancers may have left). Also, plan in advance the 8-12 dances you
would like to do, but have another 5 or 6 that you can substitute if the crowd is
collectively more or less skilled that you had planned for.