HA!! GOOD LUCK!! I am doing exactly the same, but an AMA regional event in Bradford.
Ok, last one I did in Reading was a pain.. the light is lousy and you couldn't get near the mats. I used a 70-300 sigma and ISO320 and still couldnt get shutter speeds high enough [with hindsight I would have pushed ISO's much further but was I didnt get 'noise reduction' then], as min f number at 300mm is F5 on that lens.
So, first job when you get there is to find out how close to the action you can get, and take some test shots, cranking up the ISO if you have to, but the quicker the lens, I think the easier it will be [I have decided to rent an F2.8 70-200 especially for the occasion this time]
Also, aswell as full frame shots, try and get a few close ups if you can, you know, a punch or a kick landing home - not easy, I failed dismally last time, but it was fun trying and determined to bag something on Sunday.
The only other advice is to enjoy it, and make the most of slwer bits of action, they are easier to shoot
