We campaign a 2006 325i. We have the 335 brakes and PFC 08s. 17" wheels. We don't use aftermarket cooling because carbon fiber is banned in the series we run. The set up works great. We are running a softer pad in the rear this weekend though. The rears tend to lock easier. Tires get expensive and pads are worse. I would stick with the OE and try the PFCs. We run Motul Dot 4 as well. Look into Turners power steering fluid tank. If you don't fab an underdrive pully, your engine bay will be covered.
https://www.turnermotorsport.com/p-9...ing-reservoir/
It is an easy car to drive but it's heavy and underpowered. We've had to upgrade to the three-stage manifold, aFe intake, Autowerks header and Borla exhaust. We dyno at 269 whp with stock internals. The other issue on these cars is fuel. They are thirsty and can't make up for extra stops with raw speed. We have a 22-gallon fuel cell that affords us the 2 hr window.
The suspension we run is a 3 way with every M3 bit you can buy on all 4 corners. It finally turns now. Good luck with the build.