If you are considering swapping your 4 lug suspension for 5 lug, a few notes about using M3 suspension.
Front - You will need the complete front struts/springs froma 96-99 E36 M3 for the 5 lug swap. Also required are the front control arms and offset control arm busings.
Rear - I do not know of any way to use the rear E36 trailing arms. You cannot use the E36 M3 differential or the axles either. The M3 diff will not bolt to the E30 subframe, and has a CV input flange. E36 M3 axles only work with the M3 diff and M3 control arms, due to the large diameter spline where it goes into the wheel bearing.
Rear suspension needs to come from a 318ti or Z3. If you can find them, and have the cash, you can use the MZ3 rear control arm which are beefier and allow you to use the larger diameter M-tech brakes.
I have another post about doing the 5 lug conversion