Dont do the H&R springs
It makes the handling worse....only makes the car look better.
Do coilovers. I assume its for the e90m3 in your sig?
Then Ohlins has the best street coilover kit for $6k...then KW for maybe $3k
If you want the car to handle better then OE = coilovers.
When your ready try
www.emw1.com in Arcadia. They build BMW race cars and maintain some pristine OE cars.