since you mentioned Hamann diffuser i'm assuming for the non M bumper. so here's our bumper as is. for the Hamann you'll have to cut and modify the Hamann to fit. I haven't seen this done recently since the F10 has been out for quite awhile but the old school guys there was actually a post on how one member did it.
Here's the Hamann installed
with that if you decide to do a muffler delete you'll need to find some quad tips.
in regards to the M5 bumper if you plan on going OEM you'll need to get the M5 fenders as well as the M5 bumper is wider than the normal F10 series (528, 535, 550). if you plan on going after market stick with the M5 style front bumpers as those will line up just fine with your stock fenders. it has been noted on the aftermarket M5 front bumpers if you're planning on putting a front spoiler there have been reports of none fitting correctly since it's a M5 Style and not actually the OEM M5...keep that in mind