You will have to get a full understanding of Fedora's installer (Anaconda, AFAIK), and it doesn't harm if you know a lot a GRUB as well. Don't swallow too much at first - go for a simple mutation that does the whole install for a core system only, not even X and GUI packages at first.
If you only want to provide a different set of packages for your distro, then modifying the installer and it's input files will be enough. You will also have to locate and replace the RedHat/Fedora owned logos and images. On the long term you will need some scripts to replace anything RedHat/Fedora specific thing with your own material.
Prepare to sacrifice a lot of time and maybe even financial resources to keep up-to-date with Fedora development, otherwise you will end up with a distro that constantly lags behind.