I have some mind boggling questions on polyjuice potion for real HP nerds.

Why did Barry Crouch Jr not look weak and hurt and sick like mad-eye when he used polyjuice potion to transform?

If I already had polyjuice potion and someone plucks my hair to add to their polyjuice potion who will they transform into?

How do I become a copy of a bald person with polyjuice potion?

If I have the hair of someone from 10 years ago, will I transform into the person now or the younger self? If that is true, drinking my own polyjuice potion can mean eternal youth?

Does the person need to be alive, for instance, can I become Cedric if I had his hair for polyjuice potion?