Well, you could use wallpaper and avoid much of painting altogether. Just print out some paper with a suitable pattern, cut in to narrow strips and glue to the walls. Then stain a bit with washes of water colour / acrylics. Should look pretty good, I do this with my WWII houses.
Depends really on what kind of interior surfaces you got. The above works for smooth surfaces. If you got panelling or even log walls, go with painted or wood colour surfaces. Show us what it looks like, and you will have more useful suggestions?
The same with the floors, if it has wood grain, paint it wood colour or paint colour. Don't forget carpets! (again print out some carpet patters).