Ethernet configuration

It really does not matter if you use the wireless adapter or an Ethernet cable to connect your client(s) to the gateway. The "network" component is the same connection in effect. The ports on the gateway are copper gigabit Ethernet ports so a CAT5e or CAT6 cable should work fine. You can use a lesser category of cable but it will not be as good for the communication. 

With respect to the WIFI you should at least make sure it is secure if you use it or not. If you live in a rural area where the neighbors are too far away to connect then it is not as critical but having the wireless radios secure so only you know how to connect is best. The gateway uses the cellular connection to communicate to the cell tower so if the weather is bad the impact could be to the cell signal not the local WIFI radio signals. If you have an issue with your PC on the wireless and it has an Ethernet cable you can use that to determine if the problem is with the local wireless. 

If you see the bars on the LED on the gateway diminished or not showing then that is a pretty clear indication that the cellular signal is degraded. To know if the local wireless is working well look at the client and see if it is connected and how well it is connected. If it seems really slow try the cable connection to the client. A direct physical connection is the most simple solution.