I LOVE Agatha. It's a total GP for me, though. I'd definitely keep it out of the FN spot, though, since almost everyone sees it as totally old-fashioned and stodgy.
From your combos I like:
Agatha Emeline
Agatha Elaine
Agatha Winifred
Agatha Celine
Agatha Sylvie
Here would be my suggestions:
Agatha Manon
Agatha Felicja
Agatha Nimue
Agatha Niamh
Agatha Maeve
Agatha Sinead
Agatha Mairead
Agatha Siobhan
Agatha Lucille
Agatha Lucinda
Agatha Fabienne
Agatha Lucienne
Agatha Maximilienne
Agatha Christie (kidding)
Charlotte Agatha
Beatrix Agatha
Lucy Agatha
Cecily Agatha
Eleanor Agatha
Elspeth Agatha
Chloe Agatha
Vivian Agatha
Ingrid Agatha
Ivy Agatha
Hazel Agatha
Nimue Agatha
Leontine Agatha
Rachel Agatha
Genevieve Agatha
Lilja Agatha
Willow Agatha