I dont know exactly how good is your knowledge on n54 engines Max...
i suggest you read this following blog:
https://bmwtuning.co/bmw-n54-ultimate-guide/
it basically tells you everything you want to know about this engine...
what makes it great... what are the negatives.. what maintenance you will probably have to do and what things may cost...
Also it gives you an overview of the tuning potential, upgrade paths and what each tuning part is for. Also lists some more popular brands for you for each part..
This might be useful when you are trying to understand the modifications done to the 35i...
overall a very good read for someone getting into n54 engines
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2009 35i DCT Havana brown with ivory white interior. Mods: Cobb stage 1+FMIC, Wagner EVO1 FMIC, BMS DCI, KW V3 suspension, M3 front control arms, Hardrace RTAB, Michelin Pilot Sport 4S tires.