I have sprayed a matt or satin finish on numerous cars. The easiest way is to use flattening base mixed in with the colour or clear. If you are planning to do it at home i assume you are doing it on a budget. I would recommend Hi-Chem (Motospray) products as they are easy to use, good quality for the price and readily available. If you are going for satin black, i would paint the car in straight colour (either acrylic or 2 pack) with the flattening base added. I don't believe you will need to clear coat the car.
Hi-Chem's flattening base is added straight to the tinter, how flat the finish is depends on how much flattening base you add. I add about 75% for a completely matt finish and 40%-50% for a satin finish but it is best to spray out some test panels first to achive the desired finish. Once it is finished you should not need to buff or polish it as you are not after a gloss finish anyway. That is the great thing about matt/satin finishes, they are done straight off the gun (i hate buffing).
The only hint i have for applying the paint is that i apply it quite heavy, being careful to have plenty of overlap on the strokes. If there is not enought overlap then you get dry "lines" along the finish of the car. I highly recommend practicing on some test panels to hone your technique and figure out the paint mixing ratio's. You might have to do it a few times but it will be worth it in the final result.
If you are using any other brand of product make sure you read the directions on the tin or data sheet as each brand will have different mixing ratio's. I'm not sure where in Sydney you are but out Penrith way i get my paint from either Auto West or KGP, i'm sure you will be able to find a decent auto paint supplier in the phone book near you.