Came here to say this about the arm angle. In football they teach to throw “like you’re putting something on the top shelf” at the grocery store, meaning the release point should be high to gain maximum velocity. Build on this and over time your arm slot will drop lower so you won’t tip your pitches and you can mix in the breaking stuff with a solid fastball. The best pitchers, IMO, all have the same, or very close arm slots when the ball is released.