I was considering buying these wheels but was unsure if they wud clear my sport brakes and if the tire sizes would work on my car. (20x9 +35 255/30/20 & 20x10.5 +45 275/30/20) I drive a 2008 G37s coupe.

 

The carid.com site says they don't fit Sport coupes, you might want to contact Velgen. Those offsets are more of a sedan offset, coupe offsets are 10-15mm less positive so a 9+25 & 10.5 +35 would be more suitable for coupe setups.

 

they are sedan offsets (off a GS350) how many mm spacers would i need to clear the brakes?

 

Bally, if you can see these wheels firsthand then you can fit this template up to be certain. Otherwise you'd probably have to contact Velgen or one of their distributors. To get a flush fit you're probably going to want 10mm give or take, so that should be plenty.
https://conceptzperformance.com/imag...nttemplate.pdf