Is it your first HPDE? If so, I wouldn't do much other than making sure your brake fluid is fresh and your levels are topped off. As you do more events and learn more about your car, you'll start to make the necessary tweeks.
Most will tell you to ditch the runflats, I disagree. For a first event, the RFT's won't limit your ability that much (if at all). For subsequent events, I would look into tires...but probably wouldn't recommend R specs until much later. The R specs are GREAT tires and will stick like glue, but IMHO they hide potential mistakes the driver can make. (A pro driver for Porshe gave me that advice very early on, he recommended suspension upgrades first.)
I drove my car stock for a bunch of HPDE's and kept working my way up through the ranks...there is not much you really
have to do until the bug bites you and get hooked.
I've since upgraded my brakes, suspension, intake, FMIC, exhaust, tune, etc. Ironically, I got a set of RFT's for free and will be running them at this next event this weekend.
Have a ball.