I'd go with Arianwen; doesn't -wyn denote masculinity in Welsh?
I think Faye is a great middle name, but I'm not sure I like it with Arianwen. Arianwen Fiona would sound better to me.
Octavia Rose is sweet, Octavia Evelyn is nice for I feel like it's maybe a bit long. What about Octavia Ellen (similar in sound and letters to Evelyn), Octavia Linna, Octavia Blythe?