I have installed TWRP onto my Nexus 7 (2012) and have gone into Recovery Mode. This has led me to be stuck on the Google Boot Screen. What do I do to fix this? I have been using this guide: http://itsfoss.com/root-nexus-7-2013-ubuntu-linux/
You need to follow a guide for the 2012 Nexus 7 instead, which the model is called Nakasi (Grouper/WiFi, Tilapia/3G-WiFi). You're using the wrong image, 2013 Nexus 7, which the model is called Razor (Flo/WiFi, Debian/3G-WiFi), for your device. That's why its not wanting to get past the boot screen. Download from the link below or go to XDA Forum.
Scroll down to the Nexus 7 2012 and select which model you have.
You can get the image from inside the program. This will run on Linux and Mac OSX. This will take care of all the commands.
Edit I did see at the bottom of the guide you used that it states for the 2012 model to use a earlier (older) version of TWRP, but it doesn't show anywhere a link to any 2012 images - just to the 2013 image.