As for Engineering, it is a department like any other on the ship. Or any ship. The Captain would be well aware of that. There are department heads, and a whole chain of command beneath them. If the top one or two are out, or were killed or incapacitated in a battle or other emergency, you don't have to send 20yo ensigns down from the Navigation department to run engineering. The ships 3rd engineer would take over and everything would continue to run smoothly.
I was thinking about this, and a large part of Kirk's reasoning in-universe was probably that he could brow-beat the 20yo (well, 18, actually) ensign into signing for the torpedoes, whereas an actual experienced engineer would probably raise the same objections that Scotty did.
You mean the cute, pixie haired blonde we saw in a couple of brief shots (one in a close up when Kirk was pleading for the crew of the Enterprise to Marcus?)Yes, I would love it if she was Rand.
I think she is s different character though. In the comics based around the JJ Universe Trek's, she goes by a different name, I believe.
If I'm thinking of the right person, you might be referring to Zahra from the comics. (Although, IIRC, her appearance has changed a couple times depending on the issue.)