Where would you put Stacks in all this?

I think Stacks is a sidechain like Liquid.

I searched nostr the other day and found some years ago there was a NIP to use names from the BNS naming app on Stacks for NIP05 (.btc and such) but that got a pretty mocking response as you might imagine.

I'd consider Cashu and Ark on a separate layer. They utilize the Lightning protocol for inter-node transactions, but they're able to function independently of Lightning as a network for their in-node transactions using their own "currency", for lack of a better term.

Actually, the other three can also handle payments internally within their own systems, independently of the Lightning Network.