For the colors I chose something little out of this world. I liked how yellow ground contrasted with blue roof. For the walls green fitted the best with purple. These kind of colors would be fitting for a witch and give off poisonous and slightly evil wibe.
What I've learned so far is to focus on strong exaggerated shape language. If you're going for low-poly 3d environments it's good to squish everything out of every vertex. Bend and twist things and do not waste an opportunity to create an interesting shape.
I think same principles can be applied to the texture creation, which I still have a lot to learn. Overall texture creation skills will benefits from all you do at 2d-level. From sketching to oil painting. It just takes lot of time and practice. :)
For further reading on stylized environment creation I'd recommend Shem Dawson's (Lead Artist at Blizzard) blog on Artstation.