Creating a custom bootable USB

I’ve been very stupid. I got an ASUS X555 laptop with 8.1 pre-installed, recovery partition etc. Like a good boy, I created the massive 32GB USB stick in case anything happened to my recovery partition (like me deliberately deleting it, with malice aforethought). I played with W8.1 for maybe 3 months, and it’s loathsome and stupid – sorry if that offends those on a W8 forum, but I worked hard...