I was just busting on Mark - I know him.
There is not much you can do about the weather conditions. You can try to choose a month that you feel is liekly to have the best wind and air tempertaures but when it comes down to it you just have to take what you get. *Most* sailors understand that there is nothing you can do about the weather and they don't hold it against you or your event.
I know I don't.

We get our insurance through US sailing -- about $800 for the year.
As far as setting a date. You really need to be aware of other schedules in the area and out of the area. IE: Nationals etc. Talk to area clubs let them know what you are planning on doing. Ask to have your event placed on their schedule or website. You'd be surprised on the good response.
You can never have too much man/women power - if they are willing to help out - get 'em. Things happen and you will always find yourself looking for an extra hand the week of the event because someone else had to cancel with an emergency.

Hope that helps some.

Tracie