I don't do much in terms of prep. I get the beats figured out, write some brief bios about the characters (as it pertains to the story), and do a lot of "What if..." exercises. Everything takes a week, maybe two. And it works for me. I've written six feature screenplays, have had two of them optioned, and have been hired to do rewrites on three other feature scripts. Yet despite all that success and accomplishment, I still get people telling me I'm doing prep wrong. So I ignore them because here's the thing: Once you learn what your style for prep is -- what works for you, what gets you from idea/concept to finished script -- it makes the whole process a helluva lot easier.

Zach, as I noted in the OP, each writer is different, each story is different. There is no right way to write. You've found an approach that works for you. Great! Anyone who would tell you you are "doing prep wrong" is full of crap and you are right to ignore them. Congrats on your success and keep doing prep and page-writing the way that works for you!

Hey Zach, sounds to me like you figured it all out. Congrats! Just don't underestimating your own technique. The story beats in combination with the character bios already cover most of the writing problems you will encounter in the process. Of course, you can always be much more detailed. Scene list, scene design, dialogue. The transition from concept to page can be seamless. As you say, it becomes so much easier once you figure out the story beats. That's what I'm still working on :D.