I like it!
The only addition I could see making would be a special movement power that helps him move over terrain to a certain height more easily (which height would depend on the height of the sculpt).
I could see riffing on Plastic Man's Bounce and Stretch:
When counting spaces for Plastic Man's movement, ignore elevations. Plastic Man may Bounce-n-Stretch over water without stopping, Bounce-n-Stretch over figures without becoming engaged, and Bounce-n-Stretch over obstacles such as ruins. When Plastic Man starts to Bounce-n-Stretch, if he is engaged he will not take any leaving engagement attacks. After moving, if Plastic Man does not attack this turn, he may Bounce-n-Stretch 4 additional spaces.
We could change the name to something like High Stepping or Stilt Walker and basically let him ignore elevations and obstacles up to a certain height. For instance, it'd make sense for him to be able to step over a Medium 5 figure, or a Car DO, but it might or might not make sense for him to be able to step over the Giant Evergreen Tree. Not sure I'd want everything in Plastic Man's power, just the ability to move over certain things easily. In fact, it should probably be part of Stilt-Man's normal movement as well, instead of a special movement.
Also, for The Bigger They Are, I think I might like it better if he compared his height to the attacking or defending figure instead of comparing the height of his base. That way the theme would still come across, but he wouldn't suddenly get height advantage on Galactus or Anti-Monitor all the time.
Just some thoughts! I really like what you have here.