Why is there no ikke here and why is there ei here?
Ikke and ei are interchangeable, they both mean not. Although you'll rarely come across ei as it's slightly old fashioned (yes, ei is also the feminine article)
Must the past participle go after the negation/before the adverb?
The adverb can be moved in this case, but the other elements are locked:
"Vi har ennå ikke vunnet."
We would more likely say won yet rather than yet won ..