I think most people where I am at (in the US) would be more familiar with
Esme for a girl, even if
Esmee is technically the female version of the name. I, too, can't imagine
Esme on a boy. I do like both spellings for a girl. It's a wonderful name!
I pronounce
Esme "EZ-may" (with the stress on the first syllable). I see you put the stress on the second. Am I saying it wrong?
Finally, I would stick with either
Esme or
Esmee, as I don't care for made up spellings. And I adore the nickname
Mae.