Do an M50 intake manifold swap first.
There isn't really much to gain from better breathing cams if the main bottleneck is the restrictive M52 intake manifold. Also, get proper software, like the Eurospeed/AA software, or the Conforti cam software.
I wouldn't worry too much about the timing chain, maybe do the tensioner. Regarding the springs and retainers, they're not necessary, but are good to do, swap for M3 or better springs. M3 spring if you don't plan on going above 7000rpm.
I already have my cams, I'm getting them installed within a month. I've already done the manifold swap
1997 Madeira Violet 328is - Carbonio Intake, Racing Dynamics exhaust, fan delete, ASC delete, M50 intake manifold, M3 Cams, Eurospeed/AA software, 3.38LSD, M3 f&r brakes + MC, Bilstein PSS, Eibach swaybars, BBS RK 17x8" wheels, Toyo T1R (235/40R17) tires, Racing Dynamics K55 kit, full euro lighting, 4300k HID lows, etc..........
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