Chin is great for first time instruction, you'll get a lot out of it.

And your autocross skills will actually serve you quite well on the track. You'll have a better idea where the limits of the car are than the average joe who just shows up with nothing but street driving experience. It's a pretty well known truth that track drivers who started out as autocrossers almost always make faster track drivers, and track drivers (without prior autox experience) make crappy autocrossers.

Sebring is hard on brakes. You've got a really heavy and really fast car, so it wouldn't be a bad idea to put a set of track pads on it. (not "performance street pads", but actual track pads) Whether you do the pads or not, definitely flush the brake system with good high-temp fluid.

Having some familiarity with the track will help, search for videos of clean well-driven laps and watch them while studying the map. Other than that, just listen to your instructor.

Biggest difference from autocross aside from the higher speed and danger level is that in autocross you focus about 95% on the course. At the track, you have to focus on the course, but you also have to be watching ahead and behind for traffic, and spotting each corner worker station as you approach it looking for their signals. If you can master that and drive a decent line, your instructor will love you!