If you are using a Gateway, you should set up the Gateway first. Once the Gateway is operational, each node should be commissioned near to its final installation location. This will allow you to test the radio signal strength between the node and the Gateway to verify you will have successful communication.
It is not required, but it is helpful. When the Gateway is first powered up, it first checks for a hardwired LAN connection and if it doesn’t find one, then looks for a SIM card. If it does not find either, it goes into standalone mode. This setting can be changed by hard-wiring your PC into the Gateway and changing it or by powering the Gateway off and back on, but it is simpler if it is connected to the network during its initial commissioning.
Yes. Data traffic for the Gateway must be enabled through SSH port: TCP 22.