Thanks guys, I appreciate the kind words.
As promised, the back seats have been installed.
They went in quite smoothly, except that the back is a bit tight between these armrests. But apart from that, no problem at all.
I just raised the seat about 1,5 mm to make it fit better against the front of the armrests.
So here are the pictures for the time being:
Next up: the dashboard. This will be fun to do!