howsit, most of your questions have been answered previously, but since the search was giving us issues at some point I am not sure if it has been sorted out yet.
Things to look out for is the service history, have an idea of what was changed on the car and when, front suspension bushes will need some attention post Motorplan, dampner pulleys closer to 200k km, if car was not maintained and decent fuel used then injectors could also become an issue.
The pre lci have been known to suffer from swirl flap failure, but not so much the lci. I stand corrected, but the flaps are on the intake and regulate air and affects efficiency on cold starts.
There are many that blanked off the EGR, both using the pipes and via software, most tuners do this anyway.
AUX can be retro fitted, not sure about USB though
Could be a number of issues why the car is lazy, but it should not feel slower than your 2.0d. When i first got my E60 i also didnt think it accelerated that fast, but the speedo told me otherwise. Remapped they become a different animal.
I stand corrected here, the odometer can be tampered with but the actual mileage is recorded in more than one location that all cant be tampered with.