I love the television series. I've never read the books. That said, I don't think I'd join a GoT roleplaying site. It's hard enough keeping up with Harry Potter roleplaying sites.
Sounds good as long as you can get the plan in place and put it into action. I seen many successful RP forums done right, but the question remains is if you can do the same? If you have had a extensive previous history with other RP forums and know how it works then you should do fine, but only time will tell.
I am not a huge fan of GoT, but I know of it played the Telltale game versions of it and know some of the popular characters thats about it.
However it turns out I wish you success with your RP forum though. @WLTG