What does "flying up" mean? Taking off (in a plane)? Gaining altitude?
I remember "fly up" as a ceremony in the Girl Scouts (US).
Gaining altitude or flying up onto/into something (eg.: the top of a building or a tree.)
Planes taking off is felszáll.
At least in English, I can also fly up to Canada for the summer and fly down in winter (either on an airplane or if I were a bird)
Doesn't need to be.
Usually you add personal pronouns at the beginning for extra emphasis, but this isn't the case here. Mi is added here because is needs a (pro)noun to attach to. You could also say "Mi is felrepülünk."