I'd do this:
Ethernet over your power lines:
One at the router, one where the printer is. EDIT TO CLARIFY: You don't need two kits. One kit comes with two modules. One module goes by the printer, the other by the router.
Then, to get your 2nd port at the place where your printer is (one for the PC, one for the printer) use a switch:
You'll use one port on the switch to hook up to your powerline adapter, and then have four remaining. Two to use, and two spare in case you need them. You can go with an 8 port switch for not much more money if you need more future-proofing.
You could use your Belkin router in place of the switch, but you'll have to make sure you turn the DHCP server off and only use the LAN ports.
There's also the option of running a cable instead of using the power line adapter... Ehternet is good for up to 100m. But that might involve drilling holes and/or having a cable snaking around which you might not find acceptable.
As to your question - WAN is Wide Area Network, or the Internet. LAN is Local Area Network, or your house. Residential 'routers' are actually a Wireless Access Point (WAP), a firewall with Network Address Translation (NAT) capabilities, a DHCP server, an Ethernet switch, a router, and sometimes a traffic-shaping quality-of-service (QoS) appliance all in one box. The LAN to WAN layer passes through the firewall. Usually the firewall will reject unsolicited outside traffic coming in on the WAN port, and keep track of what is talking on the WAN side. Since it's tracking what requests are made from the WAN side, it can send expected traffic coming in from the WAN side to the correct LAN port when it arrives. So if you're using a router as a local device, this could wind up acting like a one-way valve in your network, so the printer can talk to devices but not the other way around, or vice-versa. That can cause some frustrating and weird problems if you're not sure how the network is set up and/or why it's acting funny. Things on LAN ports don't need to go through the firewall when they're talking to each other