Well, it's already over 100 pages long and I'm not going to read it all or answer them all, but I saw a general doubt among people as to why Zoro needs to discover King's body.
This I explain to you.
Oda works the concept of swordsman's strength differently from the others, which is just brute force, as in Luffy's case. For Luffy to get stronger he just needs to use a stronger haki or have a stronger transformation.
The swordsman's power is different, as already said by Koshirou (chapter 194) or by Hyogoro (chapter 939), the real strength is to cut what you just want to cut.
Remember that when Zoro defeated Mr 1 he first "heard the breath of steel", he understood the properties of steel and thus transferred his desire to cut it to the sword.
This is the secret of a swordsman's strength in One Piece, understanding the properties of what you want to cut and passing the will to the sword through the haki.
We see a clearer example of this in Marineford's war when Mihawk attacks Luffy and Daz Bones interferes, at that moment Mihawk couldn't cut him because that was not the intention, it was a blow to cut Luffy, right after him deals a direct hit on Mr 1 and defeats him, because at that moment, that was the will passed to the sword.