Hello,
My mother come from benin, I've lived over there.
I ve read your message, most of infos that you give are right but there are some mistakes.
Abomey was a fon country not Aja even though Aja is close to Abomey so there's some ethnic differences.
Twice, the name of the king that you give (son t remember exactly) is untrue.

There's an excellent book about this subject but it is in french and I don t know if there's an US translation.

It's "peuple du golf du benin" by François de Medeiros.
You can try to find it. It relates the formation of this country from middle age to now

hope it will help you!