Question about eufy HomeBase S380

I didn't understand it that way. But placing different home bases near the distant cameras helps.

Not really link them together. But you can assign different cameras to the two homebase. Then link everything in the app.

I have no information on this.
However, it should be enough if the network (possibly extended with mesh) reaches as far as the cameras/sensors etc.. These then connect to the home base via the network. At least that's how I understand it.