I would spell it Esmée. Esmé looks masculine to me.
I'm half French, though and I think
Esme would definitely be seen as feminine in an English speaking country. Still I think
Esmee looks nicer and more complete.
I'd use the accent if I lived in
France otherwise I'm not sure. I go to school with a girl named Céline here in Germany and she has lots of problems with the accent.