you could take the basic files of austerity (theme.rc, base.rc, plus others if you like) and just start with these. that's what i did. austerity is well structured, this can make thinks quite easier. just comment out everything you don't need, then simply start changing basics, later details.
as for the graphics, i always create simple one-color-images as "dummies", then do the .rc stuff, and finally change images again to what they should look like at the end. others first finish graphics, then do the rest. this is up to your like.

(is that right: "your like"? i'm not sure...)