My 2 cents...it's great to have things hardwired when you can, but if it were me, I would still want solid wifi throughout the house.
Your Asus router supports AiMesh, which allows multiple Asus routers/repeaters to work together to expand your wireless coverage. So you could put your current Asus router in the cabinet connected directly to the modem, put another Asus AiMesh-compatible device on the other side of the house, and use one of your CAT5e lines to connect one of the LAN ports on your current router to the WAN port on the new device. Once the new node is configured to know your original router is the boss, your wifi devices will connect to whichever Asus device gives them a stronger signal, and in theory at least should transition seamlessly as you move through the house. You can also use the LAN ports on the new node to connect wired devices to your network in the other room, just as if you had connected a switch. (Of course you can still add a switch too if you need even more ports.) The new Asus device could be another RT-AC1900P router, or a RP-AC1900 repeater, or any other Asus product that supports AiMesh and has similar wireless specifications. While you would have to go through the steps to configure the new Asus device, nothing would change about how you configure your laptops, phones, etc. to connect to the network.