This diagram was posted by Andy Freer on the Dash Developer Discord. It shows how the flow of Evolution works, from the end user to the Dash network. What do you think? I for one can't wait to get this purring engine on mainnet.
Your first point is true, you have to establish a link between two parties before you can by via username. However, as @GrandMasterDash said, you are free to pay to address if you'd like before that happens. As for your second point, this is the first I'm hearing about this as addresses are not static, they are constantly changing while being linked to the identity. No two transactions to the same identity should use the same address, as far as I'm aware.From what I understand, you won't be able to pay anyone via their Dash handle until you "friend" them. If this is true, I consider it a design flaw. Also, users' contact lists will be discoverable by examination of the blockchain, so that is another design flaw and IMHO a show-stopper. I would be pleasantly surprised if I'm wrong about these two points.