I have had a 2016 E400 coupe for 7 months now (coming from a 12 reg E350 coupe)
Saloon vs Coupe is simple.
Will you regularly have back seat passengers?
Space inside is not an issue in the E400 (that I have) but access is not easy, great or indeed stylish....
Apart from that, I have the run out 3.5L twin turbo rather than the 3L TT that MB started with and has gone back to, but its the same family and so far so good. I had no issues with the E350 (which was the M276 engine) and none with the mechanicals, electrics or electronics - hence I ended up just buying a facelifted one.
18s or 19s will impact ride quality (the E400 came with 19s and it is slightly worse) but does look better...
Remapping is easy (333bhp to 420bhp on a stage one), but I am not going that route - the 30% more torque this has already at only 1,750rpm is all that I need - and to be fair the rears can't keep up - though I am looking at putting new tyres on to replace the Contis it came with....
Make sure you get a pano roof or at least the half fixed glass roof the new model seems to come with - it really 'airs' the cabin.
Toys will be good in the E400 as most will be high spec (in comparison to E200 and E300's) but you may need to update the Satnav if you want to use it.
Also check if the car has Apple Car Play or Android Auto - mine came with Apple but not Android annoyingly!
Retro fitting isn't cheap!
