with system 4 you just need to attach the spacer on your factory wheel hub with the provided nuts and use your factory lug nuts:
http://d5otzd52uv6zz.cloudfront.net/...507c19-800.jpg
with system 6 you will have to take the factory studs out and install provided longer studs with the spacer and still use your factory lug nuts:
http://d5otzd52uv6zz.cloudfront.net/...cc47c3-800.jpg
if you compare the pictures for both options you can decide which one to go with easier. I would go with system 4 just because it seems to be easier and safer to me. I dont think there will be any vibration issues as long as you go with 15-20mm. if you go with 25-30mm on the front chances are you will have some vibration.