30 moons=30 months? Don't you mean 30 moons= 1 month?
1 month is the time it's take for a full moon to turn into a another full moon so 28 days
I was checking out some of the pony toys the other day at my brother's house. His two little daughters have a whole bunch of the ponies.
Twilight gave that speech to Sunset to help her develop as a character after being beaten, and no, replacing a wall is not what makes Sunset forgiven. It's her job to repay what she did to her fellow classmates that makes her forgiven. If she just replaced the wall, she would be more furious at her classmates. Also, why would Celestia talk to Twilight about Sunset Shimmer if she disappeared into a portal for several years to a land she never heard of. Unlike Sombra,Discord and Luna, Celestia didn't know where her student went. Plus considering Sunset's personality in the film, maybe Celestia never told Twilight because A) She thought Sunset would never interact with her ever again.or B) Sunset must have been a horrible student.As for why Rarity wasn't a choice. It was implied in the film that there was a Twilight doppelganger in that world, maybe Rarity had it before, and it turned out disastrous for their friendship.
The first part is a good point, but the second one I disagree with. I'd think that would have been a good reason to bring it up--what if Twilight had asked what her previous students were like? Or, alternatively, because she didn't know about Sunset's fate, it was ambiguous whether or not she would come back--so why NOT tell her just to be safe? And I'm pretty sure the third one wasn't the reason--we know nothing about human!Twilight's relationship with the main cast, and they didn't seem to know pony!Twilight when she came to high-school-world, so maybe she's a new student?