The ideal number of guests for a small-scale event is between 10 and 40 people, depending on the format:
For a round-table discussion or workshop, 8 to 15 works best. For an exclusive dinner, 20 to 30 is optimal. With more than 40 guests, you lose the intimate character.
The key is that everyone can talk to everyone without it becoming impersonal.
Read more in our article on organising a small-scale event.