Lets start from the beginning. Have you made and tested your custom kernel build? Have you packaged the kernel and other custom software into deb files? Have you tested this? Have you gotten the base install cd you want to use and extracted the ISO and cramfs (I think that's what is on there).
Also you'll need a signature if you want to setup a repo but not for a local package.
I haven't looked at the links others provided but that is probably all you need. Remastering an install cd is a pita. My preference is using debootstrap and creating an install, cheroot and work from there. You can then either use the existing install script and modify to meet your needs or just write your own pretty easy. Then distribute thumb drives with the image or look into creating a boot cd (more likely DVD) with the image. Iirc, syslinux does it on doze but I don't really remember how to do this on either platform really - I don't use CDs anymore.