I would say be careful about doing it because there are new vendors coming up all the time. While yes I would by from FL and enjoy helping the site I wouldn't do it if it cost a good amount more than somewhere else (including shipping charges) or if I needed multiple items from one place.
I'm just being honest Mike, I think if you can make it work its a fantastic Idea.
Can I also add another thought? We are a VERY large group of people, what about contacting a vendor say, kensfish, or foster and smith, or similar, and seeing if they will offer us a discount as club members? I have don't this in the past in the automotive world. While the discount was not usually a large one at least it was something. It could also be combined maybe with advertising preference to their banners and or a place that they could get betta testers for new products so that they can get reviews from a trusted source.
There were also times in the auto world that they would run club only specials say like a certain week they offered an extra % off or a free this or that, in the fish side it could be trial sized foods or similar.
An offer like that is much more appealing to me as there is also a customer service backing as well as a reputable company that is supplying products that can handle complaints and concerns. It would also not require you to stock inventory and or deal with shipping issues which can take ALOT of time out of your life.
I just wanted to comment on this- I think it is a great idea. I'm a member of another site where there have been several group buys from Bulk Reef Supply. Clubs can get group buys, I don't see why FL couldn't. The only downside is that it sounds like kind of a pain to be the person that coordinates a group buy, especially when you are talking about members of a forum vs. a club where most members are local.