Messages are end to end encrypted, I believe it is by default.

Google definitely has some metadata if you use the android app, at the very least the list of your contacts.

Regarding who you talk to, maybe: messages do not necessarily go through the servers of Google, it depends whether your carrier has their own servers.

Either way, I do see this as a great advantage over Whatsapp: while this system is still mostly controlled by Google the underlying technology most definitely is designed for decentralization and I know quite a few carriers are beginning to support it.