Hmm... there's the Tutorial subsection of Rom Hacking which has some threads about spriting in it. As for places to show sprite there's the Pixel Art part of the art sections, which also has a sticky thread on spriting tutorials as well.
And if you intend to post it on the forums, sure, and if not then probably still can! What is it about and all?
I've been doing karate for most of my life, haha. As for freerunning I've never tried it, and my backyard is bushland and many metres below my house, which is on stilts and on a steep hill. XD