Original inside piece /4 axle type Y, 1st and 2nd class

[LVG1]

Concerning your last photo, the division between the two classes was the the same point like the corridor's door. So this should be also the point were the color of the seats changes. Additionally, there were green seats in the 2nd class. Red seats were used in Z type cars but not in Y type cars, as far as I know.
And I'm not sure if the handrail in the corridor is correct. It was installed by some manufacturers but not by all. I can't evoke it for sure, but I think GDR-made Y type cars did not have it.

[LVG1]

Regarding the 2 color tone red/ brown is that it represents: red=for compartments where no smoking was allowed and brown =compartments where smoking was permitted, no matter what class designation the coach had.

So you have defined 75 % of the 1st class compartments and 0 % of the 2nd class compartments to be for smokers. I don't think this ratio will be prototypical for any manufacturer's cars.

These cars were not built only in former GDR, for a fact Roumania built hundreds of these for inside and outside use.

The Romanian-built Y-type cars looked externally very different.