Having recently looked at mine, I can tell you that the microswitch is on the left hand side when standing at the boot looking in. there is a catch and if you feel inside it you can feel the switch.
So it sounds like the plastic pin at the side of the cover is not engaging properly.
It take all sorts I suppose, when I was looking for a CLK Iwas specifically looking for wood trim as I don't like the alternatives, however I could not find one so have the aluminium trim in mine but would love the wood!
In the defence of the "injured" party, I was bumped in the rear when stopped at a roundabout, this was a very minor slight bump. On intial inspection all appeared OK but later when I opened the tailgate I could then clearly see a crack and distortion in the bumper that was hidden from view by...
I too have been looking at the dynavin for my CLK, of all the Chinese units I have looked at the Dynavin has the best user interface, some of the the cheaper ones are awful.
So, in my opinion, If original looks are important and you want a good screen display, I would recommend the Dynavin.
So, If you are serious I believe your issues have been answered.
1. The engine is the same engine in an E class as an S Class. There may be a legitimate reason for one to be swapped out ( I had one swapped out on my old E class when the Camshafts snapped - it was cheaper than getting the engine...
Not sure if you could retrofit a Mercedes Integrated system, but you could get a standalone system such as:
Tyre Pressyre Monitoring System with 4 External Sensors,PSI/BAR,Diagnostic Tools, TPMS PSI,Car TPMS 2905451 2016 ? £106.59
Plenty of others available at very different prices - just look...
I would imagine that as it is a 2016 model, it would have the Tyre Valve Pressure sensors and not the old fashioned ABS system.
If you got universal valves fitted then they will self calibrate - at least mine did when I fitted my winter wheels last year.