“went” = the trip from Capernaum to Cana is about 16 miles as the crow flies or about 20 miles by road.  The father was in a hurry to get there and probably rode a horse.  The verb is literally “went away unto him” and indicates a reluctance of the father to leave the presence of his dying son.

“The greatest men must go themselves to God, must become beggars.” (Matthew Henry)

“down” (KJV) Capernaum was on the coast of the Sea of Galilee and a lower elevation than Cana. 

In reference to the father’s faith, the People’s New Testament states the following, “Note that: (1) The nobleman has already “faith as a grain of mustard seed” (Matt 17:20, Luke 17:6) in Jesus; (2) that faith moves him to seek the aid of Jesus; (3) to make sure of his help he comes in person, instead of sending servants; (4) while he thought he could heal his son, he did not comprehend that it could be done unless Jesus came to where he was; (5) he thought it would be too late if the son died before his coming. His faith was very imperfect.”

Matthew 17:20  He replied, “Because you have so little faith. I tell you the truth, if you have faith as small as a mustard seed, you can say to this mountain, ‘Move from here to there’ and it will move. Nothing will be impossible for you.”

Luke 17:6  He replied, “If you have faith as small as a mustard seed, you can say to this mulberry tree, ‘Be uprooted and planted in the sea,’ and it will obey you.