It is a lovely name, but I do honestly think of
Princess Fiona from Shrek. But she's cool so that's not really bad.
1.
Fiona Marian Cicely2.
Fiona Dorothy Marian3 and 4. No preference
5. To be honest, the 2 middle names do not flow at all. I'll tell you why - something like
Fiona Marian sounds fine, but with another middle name that has a similar 'structure' to
Marian (i.e. 3 syllables, stress on the first), it just sounds repetitive and awkward. I'd suggest finding a diffrent second middle name which doesn't have that structure, or you could make
Fiona the first middle name, like
Cicely Fiona Marian.