I didn't realize that they have a separate kart track - that's where the karting will take place - it is up the hill on the south side of the track and there is good paved parking up there.
The 24 Hours of LeMons
http://www.24hoursoflemons.com/ will also be taking place at Infineon that weekend. This will provide another good reason for attending.
Spectators for the kart racing are free. I don't know about the LeMons race but my guess is that there is no charge.
Food will be available at the track.
Parking will be available in Lot 2.