I want to make a physics of my dress using bones and not using clothing physics. will my bones move on the dress? what if the collision on its legs moves?

If you add bones to the dress alone, import as FBX and transfer weights making it a cloth, the bones would be gone.
If you add bones to the Standard CC character and weight a dress mesh to them, you will only be able to import it back as Humanoid.

And "dress" bones converted to Spring on Humanoids, would not interact with collision shapes and dress would freely intersect with body
(unless a dress mesh is substantially distant from hips/legs, like a tutu dress).