I have the ER d-cat DP and the BMS intake - happy with both. DO NOT upgrade your exhaust until you hear the sound with the DP. I cancelled my order for the M-performance exhaust after getting the DP. Mine does not throw any CEL with the ER DP. I am running stock DME. The smell is overrated as an issue for the d-cat, a very rare and small nuisance for me. For me the JB4 has not been P'n'P - at all..., so read the forums before making up your mind.
Congrats on your M135i - you will love it
Cold start-up...