Lowering your car with ultra lows will greatly effect the wheels camber, especially with irs, making all tyres wear out quickly on the inside of them. You can fit shims to the original top arm mounts to fix this or even install a camber castor kit.
The minimum headlight height is 500mm, this measurement is taken from the ground to the centre of the headlight, or i think 100mm from the ground to the lowest point on the car.
More information about this can be found at http://www.lovells.com.au/faq.php?q=5
which tells alot about lower a Vehicle.
AU1 Forte - 17'' AU2 Tickford rims on all corners, Super low springs,
KYB shock absorbs + camber castor kit and a 3.45 LSD.
Built with spanners, not chopsticks.