On my first few resets I thought, the filming locations had to be bought in order. Also, they could have just been unlocked by the diamonds to be subsequently be bought with money like the others. Just as many people wondered, if they would be locked again after a reset. After all, you can bu one-shot options for high amount of diamonds, like money, time travel or resets.
More studios get you more stamina. But it slows down, the higher you are. And the exp per training slows down too, the higher the stamina of the girl is.
Funny thing is, the game actually gets it right with the +700%. But it would probably be better if they wrote x8 to avoid confusion.