Going Bijuu Mode makes it harder for Kabuto, not easier.But that's not the issue Kabuto's facing. If Bee enters Bijuu Transformation, Kabuto has way too many counters for it and actually, in doing that, Bee would give the advantage to Kabutomaru.
I don't see why they would.Wouldn't the Jinchūriki need to concentrate to enter Bijuu Mode though? I doubt that Bijuu Mode needs concentration once the transformation is complete, it's the transformation itself I'm skeptical about.