What are the limits of Mage’s Magnificent Mansions?

I am DMing true D&D for the first time. So far it has been one of the most fun experiences in my life. However, I have found myself in a bit of a pickle. Starting off I was very liberal in what I allowed my players to create and do, and now am seeing the problems of this break out in my world. So, now I am tightening the leash a little bit. One player in particular has a very powerful Rakshasa sorcerer and recently has started using the Mage’s Magnificent Mansion spell to create a restaurant and sell the food from inside. He is trying to weave a network of mansions from different points together to create a instantaneous fast travel system. The player states that the rules are genuine, but I’m not so sure it I agree. Are there any limits to the this spell in the rules? Can he have more than one mansion at one time and can his servants leave the mansion to act as staff in an eatery?

What happens to matryoshka Mordenkainen’s Magnificent Mansions?

The following situation happened towards the end of our last session(I am the DM): A player cast Mordenkainen’s Magnificent Mansion, so they could take a break to heal up their comrades and rest a bit.

Then, that player cast the Mansion again (after a long rest) and placed the portal inside the first mansion. Everyone went through before the first mansion disappeared, and expected to return to the main overworld again after another 24 hours.

But technically, the Mansion only expels creatures, not portals to extradimensional planes, so shouldn’t they be thrown out where the first mansion was, an extradimensional space?

I am not gonna do this to them now since this would be the end of the story and not something anyone expected, but still: Would my players be back to the extradimensional space where the first mansion was?