Did you check the solenoid part of the egr is actually moving too?
It is worth checking the top intercooler pipe,too.If it is like the 156 part of it is hidden under a cover.
It could be the boost solenoid or it's vacuum piping,not letting the turbo go to the low speed(high boost)position,this made mine smoke when I forgot to reconnect it
The actuator arm on the turbo should move about 10mm when you start the car up.It can also be checked with the free version of multi ecu scan.
I run mine on either 5w40 or 10w40 and have used semi and full synthetic,with no problems.
There is a thread on here about checking your thermostat,a search should find it
Not too sure where a tuning box would be,somewhere by the fuel rail I think,maybe?
Can't really help with the back door problem,either.
Hope a little of this helps and good luck with the dreaded MOT!