I have no knowledge of coding RVs so cant help you with that
Structures/buildings are my thing, so I will limit my comments to that (except for pointing out that the 2 yellow dots on the sides of the trams are an animated color right now, yellow flash, nice maybe when the vehicle is loading, but probably not when moving
), I think there are some others on this forum that have more knowledge about the looks of trams/trains and can give more help and more useful comments.
So, regarding the building, I like it, especially the walls facing the sunny side, that combination of grey and blueish grey really works.
I also like the red doors/panels, except for the darkest red that you have used, that seems to blend in a bit too much with the black outlines. It distorts the shape of the panels/doors a bit for me.
Try changing that red to another tone, or maybe the black outlines with something else, cant exactly point out how to change it, but I think some experimenting may be useful.
The roof is what needs some more work I think.... Dont know how much WIP it is right now, so I may be too early with some of the comments, but this is what comes to my mind
I dont know if you intend to make these buildings modular (so all one-tile pieces), if so, then I think these modules need to link up a bit better. Especially regarding the placement of the blue windows.
With the modules placed behind each other, there is a larger gap between 3 rows of windows, I think it is nicer if the gaps are all the same...
When placed next to each other, there is a dark grey gap, caused by the outer edges. Two things can solve that, either have a grey edge all around (so also on the front edges), or elongate the windows a bit at the end, making them link up with another segment.
Finally, the way you used the darkest blue at the top of the windows gives a bit of a strange effect to me, it looks a bit wobbly to me now, not like a straight line.... It depends on what kind of effect you want it to have, but it may need a bit of tweaking
Overall, I like the colorcombinations a lot, the greys and reds really work together and the blueish glass for the roofwindows is nice too!