I have done the full OEM conversion. From my perspective, you do want to have the parts that will cost you a couple of hundred extra. This ensures you have an OEM fitment, that the duct work lines up properly and that the front bumper especially is secured properly.
It is not a direct bolt on as the two bumpers use different guide dimensions.
2011 335i M-Sport Sedan | MHD Custom Tune by Wedge Performance | ER CP | Catless DP | Koni Sport Dampers l Eibach Pro Kit Springs | M3 Suspension Upgrade l BMW Performance Exhaust | BMW Performance Front Grill | OEM Euro M-Sport | 19" Volk Forged Performance ME's | JL Audio HD 900 | Morel Hybrid Components | JL Audio W3v3