MEve, sorry for the stress...I swear you will feel better soon on the sunny beaches of St.Lucia.
Here is how we did it with our group booking for our wedding in July 2011
February 2010: Engagement and resort research
July 2010: Booked Fianc© and I directly with the resort, just to secure our wedding date. (no other passengers)
June to November 2010: Design of the invitations (not including the TA info and price, but just the wedsite address.)
Early November 2010: Our passport invites arrived and we posted them ASAP
Meanwhile, I started to look for the best deal. A TA from this forum helped me and we booked with her. 10 passengers deposits were required to hold the group. I then put the info on our wedsite so people could see the price when they received the invite.
In late November, 5 passengers paid their deposits and then we paid the 5 other deposits (150.00 each). Our group rate was all inclusive with Air Canada Vacations (flight, hotel, and food.)
We had an early booking bonus December 15, so 9 other guests booked that day. We got our (150.00$ X 5) deposit back.
Then I checked the price online often to see a price reduction. With our deal, we had a chance to do a one time price reduction. Our amazing TA was able to get a lower rate, 300$ lower per person in March. Unfortunately, this new rate applies to new bookings and we were able to get that rate for only 25% of the already booked passengers. We decided to split this difference to all passengers who had already paid. They will have a certain amount on their credit card.
Now we have 16 guests booked, all with the AC Vacations package. For me, in Canada, it seems that it would have been even cheaper if I would have waited in February 2011 instead of November 2010 to do my group bookings. The AC package was really advantageous comparing to booking directly with the resort.
According only to my experience, it seems that you are very in advance for your group booking. I realized that sending my invites 9 months was even more than needed. If I were you, I would wait since the price for 2012 are not probably out yet anyways. Use the 2011 prices to give you an idea if the resort is realistic or not.
Good luck and keep us posted!