There is no official or definitive list of essentials on which we make our tests of fellowship. To a large degree, Baptists make that decision at the local level; that is, the congregation determines what they will and will not tolerate.
Yes, this is the way I have always heard it: In essentials, unity; in non-essentials, liberty; in all things, charity. It is the official motto of the Unity of the Brethren, a Christian group in central Texas whose roots go back to the Czechoslovakian martyr John Hus. (They now use the word “love” in place of “charity”.)I've always heard that saying with "liberty" in place of "diversity" and "charity" (in the 1 Cor 13 sense) in place of "humility". I think liberty is the better choice of words but may switch to humility, as that is so scripturally important.