How to stay 100% anonymous? If your life depended on it here's what I'd do.
Get a dedicated laptop that you haven't used before, that you didn't purchase with anything traceable (name, credit card etc.), and never connect to any of your own networks or networks where you're traceable from. This should be a fresh install of an OS and you should enter no personal info on this or anything that can be associated with you. Remove webcam, mic and battery.
Leave house without any mobile phone or GPS system and start driving down the street in a car with dummy license plates and tinted windows. Get something like this:
https://www.youtube.com/watch?v=iFjt5Z6lqGQ
Plug in laptop battery, turn on laptop and start searching for free wifi hotspots that don't require logins (I'm not sure if XFINITY requires a login, but if not then there should be tons of these). Pull over and connect to the network. Do all your dirty work from you car. When you're done, remove the laptop battery until you're ready to do it again.
Drive far away and switch the license plates back to your real one when you are certain there are no security cameras. Drive home.
Using a proxy or VPN in this scenario would actually be less secure because it is a middle man that could be traced back to you. Also, if you're looking to be anonymous from the comfort of your home, that's pretty much impossible.
