Casey,
I've pretty much gone down the same path. I started out as an aspiring screenwriter, even wrote for a competition once (it did not go so well). I have no formal training so tackling a full feature screenplay proved challenging for me. So I thought I would work on the finer aspects of the craft by wring shorts. One thing led to another and next thing you know I am working on my first short and directing has proved to be a warmer passion for me than writing - that said I am directing a short that I wrote.
I want to fully concentrate on directing but I wanted to have some knowledge of the other departments as well, something to help me understand what my DP is saying, what to expect from my AD, lighting, art direction, etc... I have a ton of books and DVDs that I have purchased, read and watched on the various departments (a bit of a library) and will not attempt to inundate you with them all, but here are some of my favorites that have helped me in my efforts for my first short:
Cinematography
Placing Shadows, Lighting Techniques for Video Production, Third Edition by Chuck Gloman and Tom Letourneau (Focal Press)
Cinematography Theory and Practice, Image Making for Cinematographers, Directors and Videographers by Blaine Brown (Focal Press)
Motion Picture and Video Lighting, second Edition by Blaine Brown (Focal Press)
Camera
Grammar of the Shot, Second Edition by Roy Thompson and Christopher J. Bowen (Focal Press)
Digital Video Secrets by Tony Levelle (Michael Wiese Productions)
Master Shots by Christopher Kenworthy (Michael Wiese Productions)
Directing
Film Directing Fundamentals, See Your Film Before Shooting by Nicholas T. Proferes (Focal Press) - Excellent Read
film directing shot by shot, visualizing from concept to screen by Steven D. Katz (Michael Wiese Productions)
Sound
Producing Great Sound for Film and Video, Third Edition by Jay Rose (Focal Press)
Editing
Grammar of the Edit, Second Edition by Roy Thompson and Christopher J. Bowen (Focal Press)
Creating Rhythms, Shaping the Film Edit by Karen Pearlman (Focal Press)
General
Digital Filmmaking 101, Second Edition by Dale Newton & John Gaspard (Michael Wiese Productions)
Making a Winning Short by Edmond Levy (Holt Paperback)
DVDs
The Ultimate Scheduling and Budgeting Kit Produced by Jason J. Tomaric (Quantus Pictures, Inc.)
The Ultimate Directing Actors Kit, Produced by Jason J. Tomaric (Quantus Pictures, Inc.)
Plus Training DVDs from VASST
Those are some of my favorites as far as getting me to where I am at the moment. I still have a way to go and theory can only take one so far as Directors must direct. However, these few items I listed above augmented with the valuable insight and information obtained from actual directors on this site have been rather invaluable to me thus far.
This has been a bit long winded but this is a topic that can get me going on and on. Good luck, good health and bet wishes for great success and always remember to enjoy your passion.