I had a 2nd level Synthesis Summoner take down a CR5 Eel single handedly. Luckily only two of my party are experienced players, but I do both increase monster count and add Advanced Templates to some or all. I am running a party of 7.
I am running this event at a Pirate Themed convention, and I already have the materials. As far as prospective players I do not know. There is no society representation in this area yet that is closer than 2 hours away.