I have a 2004 X5 with 255/55-18 tires (Style 131 Y-Spoke)...

1. how much of a spacer do i need to make it look good.. (i was thinking 20mm.)?

2. where can i get good spacers (where lugs go straight through spacers on to car) for a good price?

3. do i need one for the front tires?

thanks!!