With the paint,sand,paint,sand...... process you can achieve a smooth finish eventually.Just keep going until you are happy with the finish.It should work well with a smooth sided coach with no raised details to get in the way.
There must be quite a few modellers that would be happy with a non-powered set,for dragging around behind a 57.Only tail lights would be needed for that one.
As for missing details,if they are very fine they can be affected by print orientation.A very small gap between parts can disappear in some cases.
Excellent work so far,keep it up.