Can you have an aura attached to an aura that is itself attached to the first aura?
Yes, and I think you only need two Feedbacks and Aura Graft (and an arbitrary other enchantment). Just use Aura Graft on Feedback 1 and have it enchant Feedback 2.

While the rules mention that


  303.4d An Aura can’t enchant itself. If this occurs somehow, the Aura is put into its owner’s graveyard.


there's no such rule forbidding 'mutual' enchantments.