Ernie, not sure who is going to be running things, but having been in your shoes many times over the years I suggest the following:
The first thing I would do is talk to whoever runs the hotel and get them to commit to a rate now. They will be more than happy to give you a rate for a future, definite booking. They can also give you a rate break if the group exceeds so many people.
Then I would do the same thing for the boat, etc. The owners would be more than happy to quote a rate this far in advance and sometimes give a rate break as well.
I would go right down the list, item for item, get prices and rates for everything.
When that's all done you should have a pretty comprehensive list of costs... I'd even figure in the cost of little things like a new banner... or simply reuse the old one if possible.
Then I would decide if these items should be paid by dues, or on a payment schedule. A lot of people will say "yeah sure put me down... then when they see at the end how much they have to pay, they are all of a sudden busy... laugh
You could even set up payment dates to make it easier for people. So much by this date, and so much by that date...
I hope I'm not insulting your intelligence by suggesting these things because that's not my intention. But hey, it's 5:45 AM here in Texas and I have nothing better to do... laugh
Oh, Gay here is my email: email@example.com