Welcome to the team...while running shoes may not be in your plan, they really can make a HUGE difference between running in pain and running pain-free. It is really the only piece of equipment a runner needs, but they are the most valuable as well.
Running on a 0% incline is equivalent to running on a long downhill grade...therefore, many times you will find your times inside are much faster than they would be running the same distance outside.
I would also suggest cutting back your running to no more than 4 days a week so that you allow good muscle, joint, connective tissue, etc recovery. Tis better to have qualities runs then running for running sake.
That being said, every one of us is quite different, therefore what works for me, may or may not work for you since we are all just an experiment of one.
I wish you well and HAPPY SPARK RUNNING!