If it truly is your first time, make sure you go with an organization that mandates instructors in your passenger seat.
As far as helmet is concerned, buy the MOST COMFORTABLE and LIGHTEST helmet you can afford. It makes a huge difference.
In nearly 12 years of doing "this," I have never seen a cracked headlight from rocks kicked up on track in the beginner's group. When they used to tape headlights, it's as a courtesy to other drivers in racing back when the headlight covers were made of glass. When it cracks and shatters it makes a huge mess. So they tape it up so that if and when it does break, it won't shatter and leave a bunch of nasty glass shards all over the track (to potentially slice up rubber with).
Relax, get a good night sleep prior, go with an open mind and check your ego at the door, and you'll have the time of your life.
And buying your instructor a cold one at the end of the day is MANDATORY.