You do need either CAMS or AASA, this is a rule and you wont get on the track without it..
(Without saying too much, 'I Highly recommend going CAMS'.... Its easily done online.)
1st time is awesome, some of us (me) are shit slow and are only there to enjoy the day. You wont be put on the track with the big cars / drivers, don't worry.
Hit up some of the more experienced guys to drive around with you if you're a little nervous, I've been to 3-4 track days & I still intend to get a co-victim on my first go. (never done this part of the course myself)
You'll get heaps of tips and advice throughout the day when you talk all the other guys