I haven't tried it myself, but I heard that mastering Blender, learning to rig, animate and texture models to a degree where it starts looking good can take quite a while and practice. But then that's the same for every game you work on. Modifying existing models should be easier and is the right way to get started. Luckily for you, that's also perfectly legal for at least all the models which come with MegaGlest by default, since they are under a pretty permissive license.