If he's standing on the marker, he's not moving it with this intention, so I could see it being legal even if the marker does move. I'd still wonder about the issue of building a stance. I checked the decisions on building a stance, and don't see anything that's directly applicable. I do know that if you put something down to stand on, or if you alter the ground under your feet, you're building a stance, but the marker is already there.
Perfectly legal as long as the marker doesn't move. I don't think it's going to do anything to cure your problem. If anything it would simply be a less stable stance, making it nearly impossible to finish your follow through properly.
I am going to say either Beau Hossler or Cole Hammer. Both have some serious game and got exposed to some tour events at a young age. I think Hossler is finishing up his collegiate career, and Hammer is in the middle of his. I would love to see one of the Clemson guys like Stephen Behr get on tour and win a few events.
I also like these guys that are currently on tour but not "big names": Tony Finau, James Hahn, and Smiley Kaughman.