I'm in the process of building the new ArtistX ( www.artistx.org ) and would like to use DL as for the last 5 versions :-) (as always I will add a reference to DL in the Distrowatch announcement and on the ArtistX website to give DL the maximum credit). Long time ago I made a tutorial (which is now in the Wiki under "unsupported") and I would like to update it as DL has changed a bit over the last two years...:-)
My usual steps
1) lh_config and change config/ files by hand (setting only boot parameters to make splashy work and enabling the interactive build)
2) during interactive build add packages and graphic customization (basically I create a "empty" iso with the same Kde/Gnome, save home dir and copy to /etc/skel the relevant files + change isolinux splash pic + wallpaper in /usr/share/images/desktop-base and splashy background in /etc/splashy/themes)
I understand now how to use the include files using binary_local-includes/ and chroot_local-includes/ but:
1) how to use external apt sources and make sure they will go into the final iso? Need to add only debian-multimedia.org packages.
2) how to add the user artistx to various groups for making effective the installation of software like ntfs3g or other packages that require that the user is added to groups he is not part of.
3) how to test and include the new live installer (should I put the live installer udeb into binary_local-udebs/ ?)
I'm willing to write all your answers in the wiki in the tutorial and help to write relevant section of the manual about these topics so nobody should ask again to build his custom Debian.
I would strongly recommend to include graphic customizations, groups management and the installer as options of Live Magic. In that way it would become more like the Reconstructor GUI ( http://reconstructor.aperantis.com ) and spread DL also between non-technical people. I would be the first tester!