Max, welcome to the forum!
As Glendog mentioned earlier on, i have been turning my standard M3 2003, into a CSL. I won't go all out and remove sound insulation, sat nav etc but have, what i call - the must - have CSL parts. Steering rack plus DSC reflash, Wheels, engine specification (CSL cams and exhaust valves) MSS54HP ECU (all M3s beyond 2004 have it) CSL SMG software, Recaro seats, upgraded brakes, headers and Supersprint 'street' exhaust, CSL anti roll bars, alcantara steering wheel, M track mode retrofit and a few more bits.
The OEM CSL carbon airbox - installed and tuned by Evolve. Works exactly like on the CSL... perfect and smooth idle and start up. Highly recommended modification.
Good luck with your project and as for the CSL carbon fibre roof - i'm still in two minds about it.... cutting out mine and installing CSL one so the car is rigid.. is it possible? How is it done on the CSL? What has BMW used to bond that roof?