The S suspension is firm but totally acceptable.....of course if you go on a dirt road full of holes you will get your teeth rattled!
The "base"
JCW kit does not include injectors so they just swap the original ones to the
JCW head, that is why I say the "old" injectors are the same. I would not mess with them either.
I (being an old fuddy duddy) really look askance at any modification of the air intake system in a street car (race cars are a different matter). NOTHING will kill an engine faster than lack of air or crud through into the cylinders. I have kept mine original (even to the filter) and will soon be installing the
JCW 210 Upgrade which comes with a new filter and air box. I say wait for the
JCW (BMW approved) kit. Nothing like them dumb factory engineers I say.....
I have leather sport seats and they are VERY nice. The one thing that may be a problem is the wiring harness underneath the seats. Make sure the number and type of plugs are the same befor you tear things apart. The air bag system is controlled through there.
Buena suerte!