Advise

If you're using a host, you must use the client authoritative (usually for co-op, but you can also create a co-op game on an server authoritative). [client authoritative cannot be server only]

On the other hand, if you're using a dedicated server (server only), you need the server authoritative (usually for competitive games, but you can also create a small competitive game on an client authoritative). [server authoritative cannot be host]

Read up on both networking models and choose the one that's best for you. Don't forget that you can also distribute dedicated server builds with your Steam community, which will save you from paying for servers (but it is recommended to have one at launch). I would admit that for host mode, you can connect with players using the Steam lobby system, but you can also use the Steam lobby system on an server authoritative to create teams, for example.

Choose the best strategy.

Detailed documentation to come...