I think the building paint scheme looks great. One suggestion I would make would be to think about painting the roof, water tower and stairs With a weathered lok It would really make the building pop a little more. And as an added perk, I would install some outside lights. I did that to an ameritown building I did and what a difference it made. But really nice job with the painting, more so if it is your first build.
As for the tunnel, I think if you expanded the mountain on the right side down that wall a bit to give the mountain a more expansive look with the benefit of having more area to scenic.
Last suggestion - since you are in construction mode, you also might consider painting some backdrops on hardboard giving the layout some huge visual appeal.
I did them on my layout and IMO they turned out great. I went to Catholic school as a kid and I was so bad at coloring, the nuns told my parents they thought I was colorblind. My grandmother was so distraught over the nun's news, she started praying for me so God would "retun my color". Just proves if I can do it anyone can.
I watched a few how to YouTube videos and I was amazed at how simple it was to do. Only thing is I wish that I did them when I first started the layout.
I just wanted to pass along a few things I learned along the way. Keep us posted on your progress. Great start.
Ed