I’d highly recommend looking up “Situational leadership” if you’re worried about coming off as micro-managing. You need to adapt how you’re mentoring based on the mentees skill and confidence.
Coupling / decoupling at high frequencies would be a challenge for sure - but seems achievable in a world of fully autonomous vehicles that can communicate.
I don’t think the second part (about length of the train) is accurate at all. Yes, a train made of pods roughly car sized would be longer, but only roughly 3x. If you look at the duty cycle of say BART rail, you could fit a lot more than 3x trains on it. The rail is empty most of the time.