here is the base of all my rust effects:
https://www.games-workshop.com/gws/content/article.jsp?catId=cat440002a&pageMode=multi&categoryId=500002§ion=&pIndex=4&aId=15100010&start=5
The only difference that i do, is that rather than starting with dark flesh, i start with scorched brown, and the vermin brown or whatever you use in between the darkest color, and the blazing orange i *almost* do a dry brush, you can see quite abit of the scorched brown, but also the middle color. This combined with the orange, especially on edges, provides a nice "realistic" rust look on terrain.
Other than that, especially with the Imperial sector (its such a nice kit), i would stick with drab colors, lots of grey, accented with some brighter rust colors.