Whether or not you need the "3G" version will depend on whether you need to buy/download books when you don't have internet access via a Wireless Router. I have the WiFi only version and update my Kindle when I have access to my wireless network at home.
If you currently connect your PC to your router by ethernet cable, there is no requirement for that to change; the Kindle accesses the internet independently from the PC. There is free Kindle software for the PC and, if you download books from Amazon to the PC, these same books will then be available in the Kindle when it goes online and synchronises.
Does that help?