Because of pepakura's limitation I usually break each part down into separate textures. I usually gauge about 100-150 dpcm on a print (250-400 dpi), and setup the textures accordingly, keeping the resolution on a 1:1 (or even higher, often I get 2:1 or 3:1) pixels:dots. This keeps nice crisp detail, especially on curves. On a large panel, like the side of that Landraider, which is what, close to 8 inches long, you might want to go with two 1024x1024 images, along a common top/bottom line.
Not so critical on a B/W print, where you want to build up the detail with layers anyway, but still nice to have clean lines to cut on.
Tirick