im gonna be lowering my car on ark gtf springs and im wondering if i should use wheel spacers and if so what size do i need to make them flush with the fenders ?

 

I'd lower it first to see exactly how flush you want to be, IMO it's better than buying the spacers first and being off by 5mm here & there. Plus it's such a simple install that waiting is the better plan.
B2Autodesigns, H&R, and Ichiba V2 are all decent choices, might even find some lightly used ones in the marketplace for a deal.