if you want a good job,id be taking apart the wheels.Send the parts you want polished to western metal polishing and paint the parts you want done in black....I wouldnt be using powder coat.The problem with it is once powdercoated,they cant be reworked without stripping off the powdercoat(and thats a massive headache).That job should be very simple,get the centres bead blasted,use an adhesion promoter,black 2k undercoat,then 2k direct gloss over the top.With the polished stuff,its a tuff call to clear over polished alloy or not....if it does get a chip(which it will being a wheel)then you will find moisture will get under the clear and you will get powdery corrosion....it will look poo....your only option is nickle plating or elbow grease for maintanance