If you want to be a decent runner you must get out and run; the rest is just noise. Get the running in first— that is the foundation. Then: Eat mostly good stuff. Get enough sleep. Stretch if you want to— or don’t. Lift if you like lifting. Cross-train if it makes you happy. Wear minimalist shoes or big bulky ones, whichever you prefer. Listen to music when you run, or not. You can carry water with you on a long run, or you can go without. If you want to do a core routine, then do it— but first you must get out and run.