To follow on from above, this is all you need to prep for any interview in the US.
https://www.aviationinterviews.com/
I've used this site to prep for 3 interviews now, and it has always been more or less on the mark. A good deal for the $20 they ask. (I'm not affiliated with the above either).
No need to spend money on prep companies who may or may not sell you the best case scenario for you to base a massive life decision on. There are pitfalls to the E3, which have been covered ad nauseum on this thread. The airline of your choosing will get you squared away with the immigration stuff. There's enough folks over here willing to give you the real down low, you need only ask.