Q5. Who is the greatest warrior in the land?

I will answer this for the area around Candle Keep and for the whole setting.

The greatest warrior in the area around Candle Keep is probably Candle Jack. He killed the Scion founder of the Keep, a dragonborn scout, without difficult and in such manner that few of the scout's followers were willing to mount any martial objection to his usurpation. Sasha Waybright, Candle Jack's sister, has said she does not doubt her brother is the strongest warrior and has admitted that even she is scared to cross him.

In the greater empires, there are several candidates for greatest warrior. Ysan, the Dragonborn king of Hamut, whose blood has manifested more strongly than has been seen in ages and lends him a demonic appearance (red scales, horns, black claws, digitigrade legs, leathery wings, fiery aura), is known to be a brilliant general as well as a fearsome combatant. He has mastered many weapons, including his own teeth, claws, and flaming breath. Similarly, Borborygmos, Warchief of Garg, is a frighteningly strong warrior who wields a tremendous maul named Earthsplitter and has thrown boulders nearly a mile. But the greatest warrior is most likely Alcyoneus, King of Hu. His blood so strongly ties him to the throne of the ancient Giant capital that he is immortal within Hu's borders and damn near-so anywhere else.