Hi Gaz,
First off, welcome to Living Forgotten Realms thread. Once every other week, I will organize a game or two on a Saturday at the store. The adventures I run are part of the living campaign in the world of Forgotten Realms, and each adventure takes roughly between 3-4 hours of playing time.
All of your PC(s) start at level 1, and by playing each adventure, you gain XP, GP, and access to magical items that you can get for free. I would read up on the Living Forgotten Realms campaign thread on Wizards.com for more details and info.
At the moment, the next game that I am tentatively scheduling is for Saturday, Dec. 27. Usually by the beginning of each game week, I will post a muster list on this thread, and people will reply that they are going to play, and what PC that they will be using.
As for playing a Gnoll, I'm not sure if they're legal in LFR yet, but you can probably find out at the Wizards site. I recommend looking there first. All PC's can not be of an Evil alignment either. Sorry, but that's just how the rules for LFR go. And as sad as this sounds, backstories aren't necessary for this kind of play.
If you have any other questions, please feel free to ask.
~Ben
LFR Coordinator at Battleground Games