The purpose of the party is we're having an Angel Reader lady come give 30 minute readings to evryone (so there'll actually be 12 people, wups)...
Two chairs need to be dedcated to my spare bedroom for the readings (which are private) so that leaves 6 total for 'public space'.
For this type of gathering I would definitely make sure there are enough seats for everyone. If all 11 guests turn up, there will be 10 people in the room waiting. If all the guests have a 30 minute reading, they could be waiting for a few hours for their turn (unless I misunderstand the quote above). If I had to snipe for a seat for a number of hours, I'd be pretty annoyed and think you were unprepared. Plus I'd be more inclined to load my plate with food and not move out of my seat until it was my turn for a reading.