Well Solve This Equation
Did He Punch Kaguya's Hand off....NO
He used Piercing Power Not Enhanced Strength
If that Was the Case Kabuto Solo's with Chakra Scalpels
HEH!
1. yes he have punch kaguya before, and it traded punch with Kaguya by using Boling release enhanced punch. And you know how tough Kaguya is compared to Juubi clone
2 & 3. His hand is cover with Chakra that shape as claw, Although we just seeing after effect in the manga. He actually hit kaguya by his bare hand but it anhanced but chakra cover claw but still related to raw power not a technique like Kabuto
Peace