I've built a few customized Linux distros and the process it quite simple. Before you even try making one, make sure people need one
If you are serious about building one, though, I'd strongly recommend Arch Linux as a base system. Ubuntu's package manager is a pain to work with when building from source, and many packages are really outdated.
The process isn't tedious at all, truthfully, and I might be able to make one later today if you're interested in testing one out (my build process is really general and 100% automated, so including custom packages is easy).
The problem with Arch Linux (and Ubuntu now) is the DE. Ubuntu uses GNOME3 and Unity, which don't help Windows converts one bit. Arch is even farther ahead with GNOME3.2, but you have the freedom of installing basically any DE you desire.
I'm leaning towards Xfce as the desktop environment, as it is extremely
lightweight (I get about 70mb of RAM usage upon boot) and beautiful, a rare combo:
The reason I like Arch so much is because of its automated package building. There are source-based packages for Bindery, Scan Tailor and DjvuBind that automatically build the packages from source with little user interaction. Building and updating could even be backgrounded. Making new ones for BSW and other software is even simpler, as I can just modify my slew of existing package builds.
I'll write up some simple documentation for my build process, as a LiveCD/USB seems needed.