What type of joints would you use, hinge2 with suspension or a slider joint with cfm and erp set or perhaps using raycasting? How about gears, using a AMotor or setting torques/velocities manually to the wheel bodies?
Spheres for wheels or capped cylinders? A simple box for chassis, or multiple geoms?
Hinge2 already has suspension CFM and ERM. No need for sliders and whatnot...
Capped Cylinder for wheels, however, spheres work fine and are cheaper IIRC. Chassis, you definetly need to have multiple bodies there. Because, sometimes if you hit a little 15 degree slope, the front bottom edge will hit it and if the car is moving fast enough, it will send the car flying! The hardest part will be keeping the car on the ground IMO because ODE doesn't let you set the centre of gravity for the chassis. The centre is always in the middle. This means that the car will be unstable during turning. There are definetly ways around it as you will probably find out when you create your car.
Hope that helps.