I love the building. It's a cool style. The other assets around the building is fine. I do not however feel the trees fit with that style. They are quite a bit more cartoony than the building.

On your question about the border, that type of border feels like a very repetitive texture. I feel simple lineart of a page with some tears would maybe fit better. Borders are a bit tricky sometimes. If in doubt leave until you feel ready to tackle the border, or just maybe leave it.

A good start!
Again REALLY cool building.