You're a beginner, so worry about supination later. Focusing on it now can lead to really bad habits.
Your backswing, arm structure and the timing of the step and racket drop is more than enough to occupy yourself for a year or more.
Watch these two videos and follow the advice. This instructor makes the best videos on the 1hbh on youtube.
If you stay relaxed, supination will follow naturally from this. But without these fundamentals in the video, you'll be in trouble. So get first things first.
Also, my advice on grip is to make sure you are gripping the handle like you would a mountain bike, not a steak knife.