If you own something, that gives you the right to sell it on. The artist even, no longer owns his work.

The creator of the NFT can specify certain other rights when minting.

There doesn’t need to only one. There can be limited editions. Soon there can also be multiple owners of one piece.

An artist can sell more than one copy,on multiple blockchains but it may devalue the piece.

Not much to do about that but research the artist before buying.

Ethereum is most respected decentralised ledger.

Hey, there will be all sorts of legal hiccups and loopholes. And yes platforms will emerge where more rights are specified by an artist at time of minting their NFTs.

A vital element is this : the artist and collector have a connection via smart contract . The artist most likely can be contacted for questions by a collector.

Just roll with it. It will all evolve.