Kishi has kept the details about it confidential, which i think means that it will play a big role as to why the uchiha were massacred, do you think it was important?
What meeting ? Danzo and obito never met up to have a conversation and the massacre has already been explained the why and the how
Nah, besides, it might just be that Obito wanted to make Sasuke even more hot headed, and increase his lust for avenge. We saw the rush Sasuke got from gaining vengeance over Danzo. That was Obitos goal.