As much warning as possible is appreciated, however 2-3 days is OK in quiet season or at least a week in Nov-March.
How many glasses should I allow for?
Depends on what you are serving, how long you are serving for & whether or not you have washing facilities. In general though you should allow 1-2 glasses per guest.
Do I need to wash everything?
No just rinsing the equipment is OK. (It should not be returned dirty or a fee will be incurred)
How many people can I seat around a 1.8m long trestle?
6 - 8 people
How many people can I seat around a 1.2m round table?
4 - 6 people
How many people can I seat around a 1.5m round table?
6 - 10 people
How many people can I seat around a 1.8m round table?
8 - 12 people
What distance do I need to allow between tables?
1 - 1.2m. 500mm per chair (back to back) + 200mm space for movement.