You won't have a problem finding a seat on either the front stretch or the back stretch if that is your preference. You will probably be around half way up in the grandstands though at best. As a word of advice, you might want to consider sitting on either end in the turns. 500 laps of turning your head constantly can be a real pain in the neck.
All of the seats are reserved seating so no matter where you decide to sit that is how they are sold. The only reason to buy ahead of time would be to avoid the lines at the ticket windows. If you arrive early enough on Saturday you shouldn't have a problem. Should be plenty of tailgating in the parking lot for your enjoyment.
Enjoy the race and if you have time stop by the Checker'd Past compound by the purple palm tree. Lots of racing talk and some BS will be flowing for sure.
You will find some of Anderson's finest rubes hanging out there.