Not using TURN and STUN specifically as the RFCs, but in effect it's the same. Routing will STUN (establish a direct peer-to-peer connection) so long as either side has full cone NAT.
As a planet, you need some star to route for you. Right now, the network is small and friendly enough that trust problems aren't an issue. As we grow, we'll put in an escape protocol so that you can switch stars if you have an issue -- there are 2^16, after all.
Urbit is not PGP. It's designed to feel more like the early Internet, ie, a wide-area world of nontrivial default trust. At present, it would be foolish to go full cypherpunk, because we're a long way from being worth attacking.
Hoon is unusual, but I wouldn't call it "esoteric" -- that term is reserved for languages which genuinely don't care about usability.