If I’m following your questions, the “uplink” / WAN port you’re looking for is just the coax connection. That is what your gateway uses to communicate with the outside world. (Edit to add: it used to be more common to have a separate gateway/modem & router. In that case, the router would have an uplink port which you connect to the gateway. Nowadays they are commonly in the same box, often along with a wifi access point)
The rest of the ports on the gateway should be LAN ports. So you would run one of those into your bedroom as you describe, connect that to any of the ports on your switch, and then plug your devices into the remaining ports on the switch. If you don’t need/want any fancy management, an 8 port gigabit switch is cheap.
With most switches, it does not matter which port is which, but some may have a specific uplink port–if so, you would want to connect that to the Xfinity gateway.
If you meant to attach a photo, it did not come through.
Generally the benefit of the mesh systems is that you plug one module directly into your router and the others will connect wirelessly to that one to extend your coverage. So you don’t need to worry about anything except a wall outlet for power for the remote modules.
Without photos it’s impossible to say what all might be hooked up to your router. How many wifi pods do you have currently, and do they all have an ethernet connection to your router, or just one?