You can play around with Arch, LFS or Gentoo in a VM or you can install it
to usb. That way you can take as long as you want to learn. The problem that
you are going to have is that you need an internet connection for most
distributions because of how it is distributed.

There are alternatives to KDEnLive. There is PiTiVi, Open Movie Editor, and
Cinelerra (in order from easiest to hardest). You could install a basic
distro such as Lubuntu which is lightweight and install your movie editor.
Remove what you don't want and use Reconstructor to build a Live CD or ISO
which you could install on a usb stick. Make sure you have a fast one and
one large enough to fit your temp files. It really is not hard to do.

The nice thing about Linux is you can do pretty much what you want and most
people do manage to use it in diverse and interesting ways.