Hi Ace, I think you have a good start to your build. Things you might think of adding are trim to inside and outside (Don't forget ceilings it really helps add detail.) Things like air ducts, lighting fixtures, and on the outside, signs, posters, occasional highlights and color changes. If you look close at a structure..lets say like Wal-Marts, they have little flares of color that help bring life to the build, and if done carefully, they will not take away from the realistic look of it!
Good luck and keep up the good work! :D