Point 3.: I've filled up the 3 addresses, as it's what the instructions mention, not one only 😋. And right now my memory is that those addresses were already "populated" when I created the referral link, thanks to the Keystore integration.
Point 4: as far as I know, THORChain & Mayachain are not EVM-focused, so Metamask wouldn't allow you to manage those other 2 chains.