[whswhs]

There is an underlying common skill, but it's not Thaumatology; it's Ritual Magic. That is, it rests not on the study of an impersonal force or power or attribute such as mana, but on social transactions with the spirits of the world. Paths default to it at -6 (though Books, canonically, do not).

If you are an elf, and you have Ritual Magic-14 and Path of Making-14, you have various rituals at 14 down to 6 as defaults. You have Path of Herbs-8 as a default, and various rituals at 8 down to 0. You have the dwarves version of Path of Making at 11, because you aren't familiar with the peculiar dwarven styles of doing things; you have its rituals at 11 down to 3. But you have the dwarven Path of Stone at 5, because you have both the cultural unfamiliarity penalty and the default skill penalty; and your very best ritual default is 5.

The kind of path overlaps you're asking about, like Cunning and Hunt, or Hearth and Habitation, are handled by having paths with different names and root concepts share some rituals. For example, the Hearthstone ritual occurs in both Hearth and Habitation, though the version in Hearth is also used to help set up a kiln or smelter. There is overlap between rituals even for the same species; for example, Path of Dreams and Path of Making share a couple of rituals.

Path of Form is indeed the shapeshifting path.

I think that addresses most of your questions?

Bill Stoddard