The group of people watching Prince James fight the brute don't appear until after the brute falls to the ground. If they were watching the whole fight, as the scene suggests, they would've been visible in several shots.
When David returns home, it is local to Storybrooke (he later walks to see Mary Margaret). The town is supposedly very small, with only one law enforcement officer. An unknown person in a coma would be big news and covered by local media, to include a photo. For example, when he returned home, his picture was on the front of the newspaper Mary Margaret was reading. As such, his wife would have known where he was. This exceeds the normal suspension of disbelief required for fantasy shows. However, Regina could have easily kept this from happening with the Dark Curse.
The Prince's armor is the same before and after it is damaged.
The prince declines to shake the hand of King Midas, ostensibly out of fear of his golden touch. The prince was wearing a gauntlet, and he was holding the sword Midas turned to gold, so he could have shaken the hand of Midas with no ill effect. However, it could be that he doesn't want the gauntlet turned into gold.
Charming/David both in the past and present wears the Guy Perpetually in Need of a Shave facial hair. While it has been in vogue in modern times, in the period for which Charming existed, men either wore beards or were clean shaven. However, this happens in a magical realm that could easily have had different rules.