Am I over-exerting myself?

There is no too much unless the sum of it all causes you to perform less then fully at any one task.
If training and running the Army 10 miler means your skipping out on work call formations, leaving your fellow SM to pick up the slack, yes its too much. If your getting up at 0300, running sprints, going to PT formation, working all day with your unit at your assigned tasks, taking a power nap at lunch after eating your planed diet noon meal, working all afternoon with your unit, changing after released for the day and getting in your distance run.. AND able to do it all again tomorrow ,,,then no not too much.,

When it comes to your current unit, they will love that you represent them so well, and will likely put you at the top of lists amongst your peers for consideration and selection to advanced schools, promotion, waivers etc. I once sponsored an E-5 to the E-6 board, and because he had successfully run the Battalion Remedial PT program, aced previous Soldier boards, and a few other things in the Bn; his E-6 board consisted of "Hey, I already know you are stellar. You're recommended, get out of here.", which took all of 2 minutes, and I was barely able to take my seat.

That being said, its always important to keep everything in perspective, and not allow the fast track to give you a false sense of accomplishment. Rank does not always indicate competence, and other Soldiers can tell when another was only fast tracked because they played the "game", and whether they are truly competent individuals, and the "game" was just an added bonus to their well-roundedness.

Be that PV2 who not only represents the unit well at events, but also performs exceptionally well at all aspects of your MOS and Soldier skills. That is how you fast track and make the largest positive impact in the Army.

That's just my opinion though.

My advice is its awesome that you want to fast track, but just make sure you don't overwhelm yourself in the process. Take in and learn as much as you can about your job and the Basic Army skills and everything else will fall into place, and best of luck as well! Your the type of Soldier that every NCO wants who is motivated from day 1 and wants to better themselves. My last duty station was Wainwright and I did the ten-miler as well...finishing that was one of my proudest moments, same with passing the promotion board and graduating BLC.