When it comes to the manifestations, I just have faith that Bahaullah knew what he was talking about. I understand that a large number of Buddhists are atheists and that logically opposes the view that Buddha was a manifestation of God.I am a Buddhist.
An utterly atheistic and anti-theistic Buddhist, to be exact.
I think the best we can do as bahais is find points of unity where we can agree and not focus on the parts we disagree since that is probably not very productive for either side