Well here's my two cents...
When you book directly from the resort, the prices are ridiculously high. I believe a travel agent is the best way to go IF they are with a company willing to price match! When my TA gave me my first price quote, I thought it was quite expensive, but it was still less than what the resort offered. So I checked travelocity and expedia for prices and it was about $600 less than my original quote. So I told my TA, and she did a price match and it ended up being about $900 less with a non-stop flight.
So even if you have a TA, look up quotes on your own on those websites, so that they will price match. If they refuse, then you shouldn't book with them because it seems that they're more interested in making money than helping you.
Another thing is, are you sure that your guests will be staying for a whole week? They may only want to stay 4 or 5 days so it might be cheaper for them.
You definitely don't want your guests to wait to late though, thinking that the prices will go down. 8 months before my wedding, prices were dead cheap! 2 months later, they'd doubled! So try to find out whats an average price for the time of year your going... And make sure you tell your guests to purchase travel insurance! You never know what can happen and if they find out later that it's to expensive, they can get all their money back, minus the insurance cost.