Qualifications
You need to be a triple threat: You should have experience with criminal trial law, have experience with written and oral appeals, and be solid with federal rules concerning evidence, procedure, and sentencing (source).
You will be vetted (and no, we don't mean you'll need a rabies shot). A couple of FBI guys may go to your law school and neighborhood asking around about your character. It means the IRS will audit your taxes...with a fine-toothed comb.
Your credit will be looked at. (Better hope you didn't max out your card on that new car or forget to pay a bill or seven).
After a preliminary examination of everything you've ever said and done, you will become a probationary employee for twelve to fourteen months. During this time, they will dig even further into your past to find out everything about you. If you've done anything stupid, like brought a goat to school or thought wasabi was pistachio ice cream and eaten a big hunk of the stuff...they'll find out.
You'll need to be able to handle anyone and anything...especially the truth.