Susannah Olwen is gorgeous.
I really like
Nolwenn, but I think that
Susannah Olwen sounds much better.
Susannah Nolwenn has too many N's. I would avoid using a middle name beginning with N.
Iscah is an intriguing name, but
Susannah Iscah is a mouthful.
I like
Blanche, but
Susannah Blanche has too many "an" sounds.
Although
Susannah Belle flows nicely, it's too cutesy.
I don't care for the sound of Tacy.
These are my favorites:
Susannah IrisSusannah Eirys
Susannah LarkSusannah Pearl Susannah Vered