Im in the process of the same thing. but for the e92 335i. Got an absolute stonking deal on a 99.8% complete M3 subframe and suspension.
Im going to be attempting to install the ENTIRE subframe, but with different rear springs (to match the eibach ones in the front of my 335i). I just need some of the perches, rubber mounts, covers for the springs and shocks.
Other little things that I've found out are that if you cant find a M3 propshaft, one of the older e38 / e39 v8 (not M5) ones should match up (although the pre-installed bolts need hammer out and e92 M3 ones fitted).
Since im putting in the whole frame but keeping the 335i rear brakes I will need to use a custom toe arm, but all the other arms fit.
Hope some of that info is useful across the models?