First part.

Interesting pov, if we hold the tannakh/Old Testament sources as historically/demographically 'truish', you are probably right.

Second part.

From what i know, Khazarians were converted to judaism much much later on by unidentified semitic jewish merchants/migrants coming from the caucasus. Until then they were a nomadic/tribal turkish animistic people from central asian steppes settled among eastern ukraine, the north caucasus and the caspian region.