UPDATE: See comment section below this post.
This guide is so complicated because the iMac's 27" Mid 2011 SuperDrive doesn't recognise the windows install disc. It's useless.
IMPORTANT: Unplug all external and physical hard drives (where possible) that you won't be installing to to avoid accidentally erasing them. Also make note of which drives and partitions remain (e.g. System and Storage hard drives), and be super careful to not erase the wrong one.
RECOVERY: If you nuke your machine, restore your time machine backup. Instructions here.