Does anyone have advice for me on how I could arrange my dark and light fabrics for a scrappy log cabin quilt?

From what I can tell in that picture, it doesn't matter. If you want them arranged with a light half and a dark half, pick two sides for dark and two for light. In the quilt in that picture they ignored light/dark and just added the strips to give it a more uniform look and not a definite light/dark. The main thing if you're going to do light/dark is ignore the colors and just sort into light/dark.

Thanks for the advice. When I pair the light/dark fabrics, does it matter if for eg I have two white strips or two red strips side by side? I think as long as I keep to the light/dark theme, the colours don't quite matter?

'Zactly! You might think it looks wrong or something in the individual block but once you get the whole thing set together and quilted it'll look great.