One way to divide packages, is to do it by categories, "Section" in Debian-speak. Doing it incrementally, one may add packages by category, and at one point where the compressed image attains a critical size, break off and compress it. Then add a large (say 6-10GB) persistent store, continue with installs, which then will be done to the persistent store, and at the end compress this as a KNOPPIX2 cloop image. Repeating the process as necessary.

This is very actual with the version I work on now, dividing into basics and sci/math. So that most people would live well with one image, the first, but the second is stuffed with tools. I have just reached ca 20 GB installed size, after adding a majority of 64-bits sci/math Debian packages, to test this out. With one image first, but then with two or more.