since we didn't really get to see them interact outside of group scenes, how do you think Brainy and M'gann would get along with one another? Would they be friends, or could M'gann be wary of him at first? (maybe she's heard some stories about the original Brainiac, so she could be cautious before actually getting to talk with him)

Honestly, I feel like M'gann and Brainy have too much in common for her to ever feel wary of him. As a White Martian, she also experienced a lot of judgement simply for who she was and wasn't immediately trusted by anyone. She even presents as a Green Martian in battle which could serve as a parallel on Brainy's own journey from blue to green.

I especially like the conversation M'gann has with Nia in 5x19 and how she encourages Nia to look deeper into her dream's meaning surrounding Brainy. She wants Nia to hold out hope for Brainy and even uses herself as an example about how J'onn had initially been distrustful of her before her true intentions were revealed to him. In that way, I think she and Brainy would be able to bond over their shared struggles and would probably cultivate a very quirky friendship.