It'd be cool to have Crystal as the focus character/lead, just to give superheroines their due. The only problem with Crystal in the MCU is the lack of Johnny Storm (and the rest of the FF, for that matter)...at least for now. She's kind of without an anchor.
Maybe Medusa would be a better focus, as BB's wife, and the only one who truly understands him.
But I really think, if you don't make BB the actual lead, that Karnak would be a better choice. He serves as team mentor, and he's really the most "human" of the Inhumans. Badass kung-fu fighter and philosopher-king with some awesome tats.....? He's tailor-made for Hollywood.