Jimmy, I'm glad you found the tong progression picture useful. It's been invaluable to me.
I've have also experienced the wrist tiredness that you mention, I think part of it is not being used to the weight but a larger part is overgripping the handle. Hofi recommends in his BP BP1002 Hofi Hammer Technique*-*I Forge Iron - Blacksmithing and Metalworking to hold the hammer very loosely, to the point it's almost going to fly out of your hand as you swing it. As I'm still nursing my neck back to heath, I haven't been able to try that technique but plan to as soon as I can hammer again.