I watched the first two parts (just ran out of time for the third). I knew all but one song on the radio.
I was confused, I thought this was the swarm you were talking about before. You said nuc, I was just distracted and didn't read your post properly (we had a lot going on around here this morning), so sorry about that. That makes me a little less enthusiastic about the speed at which they are drawing, but I still think that empty deep in the middle is fine. They looked like they needed the additional room, and putting that in the middle should encourage them to work it. I also think removing the entrance reducer is fine at this point. How big was the larva in the queen cell? Or was it just an egg? A single charged cell is risky to remove, as they may just be superseding the queen, not swarming, but on the other hand, they are building a lot of cups and they seem to have plenty of other eggs to choose from at the moment. Since you have the swarm to fall back on if something goes wrong, you could take it down and see if they charge more. It depends on your goals and whether you'd rather risk losing a swarm or risk them going queenless.