I don't know jackshit about these things, but I have a lifetime of overthinking. It's best to pick out what you are going to do from the advice you have here and set your mind that way and keep thinking about how great that plan is going to be and how it is the best course of action.
You are clearly motivated and want the job, and that's why you are overthinking. You want to do well. Go look in the mirror, compliment yourself, build yourself up, reflect on your biggest accomplishments and go fire up that email. The hardest part is doing something, once it's done, it's done. Find the best version of yourself, present it in the best manner you can, and go get that rough ridin' job.
Also, I vote for pissclams advice.