Question: Why did Daniel and Ethan fight on the train hand-to-hand, instead of using guns? (02:16:00 - 02:20:00)
Answer: Maybe they didn't have any guns at that point.
Answer: In an enclosed place, a bullet can ricochet around until it hits something - one of them or an innocent person: man, woman, or child. Worse, it could hit a section of the train, a brake line, a cable connecting the cars, or one of the conductors.
Question: Was Kittridge a good guy or a bad guy? I just couldn't figure him out by the end.
Answer: He's not a bad guy to the extent of murdering and plotting against the good guys, but he's not exactly morally upstanding either. Kittridge doesn't want to destroy the Entity like Ethan; he wants to gain control of it on behalf of the US government and is happy to deal with the White Widow or anyone else to achieve that end. His appearance on the train isn't especially nefarious; he's just the highest bidder.
Answer: He's either.
Answer: While it looks like a normal Fiat 500, this is a specialised IMF car, as evidenced by the controls inside and its ludicrously high speed. It being electric is in line with that.