For BM3 stage 1 there is NO requirements for mods, i.e. a stock car can go to stage 1 immediately. For stage 2 a FMIC and Downpipe is rec to get the most out of your tune. Each different tune thereafter might require supporting hardware before you can fully maximise it.
You can also request for a custom tune where you give the tuner your hardware upgrades and they can customize a map to your individual requirements (this cost more).
There are multiple updates even for stage 1 maps changes are normally boost control timing etc etc you can check the change logs. It is NOT install and forget as there are constant changes for even off the shelf maps which improves HP torque drivability.
All information is available do read up as you go along as most people who go to a workshop to get BM3 will have little understanding behind each individual tune and its requirements. Do remember at the end of the day that the n20's engine is limited and things like the arama intake as well as the exhaust will not make much of a difference but will cost a lot !
The stock BMW intake is actually very good if anything a drop in k&n airfilter is sufficient to improve breathability. The stock box also is a cold air intake somewhat and will not suck in hot engine bay air unlike most open pod setups.
If sound is all you want, and you can do something else better with 3.2k for a simple axel back exhaust just increase the volume of the active sound, so called fake exhaust sound coming from your speakers can be done with coding.
If you're looking for pure performance gains stick with the following
Wagner Intercooler - $1600
ER Downpipe with racing cat - $1500
BM3 stage 2 tune with 93ron (98 octane)
Operate stock exhaust - $??
Any 98 octane petrol - $2.4/L
K&N drop in filter - $1xx
Better or wider tyers
BM3 change logs and updates
https://bootmod3.atlassian.net/wiki/spaces/BCS/pages/485130241/bootmod3+Release+Notes
Full Diagnostics and Coding and battery registration
https://www.mycarly.com/
Codings by Bimmercode get the OBD reader and app and DiY
https://bimmercode.app/cars/f32/
Intakes