- No fees for coordination apart from transaction fees which goes to miners
- Yes
- Not possible right now but I can make it configurable
- Yes users can also use multiple relays. Once the process is initiated, joinstr client keeps looking for events regularly and moves to next step when enough participants register UTXO
- Paid relays and encrypted channels will reduce lot of attacks. There are a few other ways which can be experimented once it's ready for mainnet.