Welcome to the boards, William. I'm an aspiring (perspiring) writer as well. You're absolutely correct about On Writing. I've got the hardback and the audio versions and have been through it many times. Anytime I hear of someone who likes to write, I encourage them to go for it as much as possible. If you enjoy writing, there is nothing that equals the satisfaction that comes from it.
On Writing was the first King book I ever read, about 10 or 11 years ago, and it made me curious enough to read more, starting with The Green Mile. It's been one after another since then.