Another great how to vid on the whole process.
I'm sure he did a fatigue study to the parameters of his E46 subframe in relation to the chassis before install too
You can do the install with the subframe in the vehicle but I removed it as I am also fitting solid subframe bushings, solid rear upper inner control arm monoball bushings and solid rear trailing arm monoball bushings and it is just easier to drop the entire subframe if you are doing all this. No you do not need a lift, it can easily be done on jack stands.
The E46 platform is notorious for chassis quality issues. Most people have never changed their diff bushings and they are still running the factory rubber OEM type bushings. Does this then mean that the soft OEM rubber bushings caused the structural problems in the E46 chassis that they are experiencing?
I would say, not entirely because the primary issue is with the weak E46 chassis that has a large amount of body flex compared to the Z4M chassis, especially compared to the structural rigidity of the coupe version. Simply blaming chassis damage and cracks on OEM or solid bushings is probably not entirely accurate or realistic. In either case, that is not the main reason people normally install them.