If you have a bigger rim and lower profile then OEM you already have a harder ride. Once you lower it each tiny pot hole you drive over is going to feel like driving over a crater, and the lower you go the worse it is, and if you have a bodykit that sits real low you may well damage it on speed humps and large pot holes. A real low ride looks cool, but aint always good for your ride, if you want the car slammed to the deck then you may want to save up your money and sit the car on air.
I would also advise to fit some polly bushes if you are going that low, as the OEM ones may not be up to the lower stance of the car.
Once done you need to get the car on a laser tracker to get your geometry set up, otherwise you are gonna be buying tyres all the time.