So the usb isn't booting?
As a rule, don't try the same thing twice. And don't change too much at once. If the usb was working, then the usb isn't the problem.
We all know what you're going through. In the end you'll wish you had just saved up the money to buy a mac. Especially with this old machine we have.
This a typo?
Should be /Volumes/USB/System/Library/Extensions/
maybe try deleting the old one first to make sure it's not just making a duplicate or something. Then own it afterwards.
Still no luck? It's complaining about that kext.
you can check permissions with
ls -l
or
ls -lr for recursive (maybe R)
so
ls -l /Volumes/USB/System/Library/Extensions/*
and make sure that kext has root:wheel in the details