The Hopi women's hairstyle thing seems to be an afterthought on Lucas's part; he never mentions it in interviews from the time of the original 1977 SW.
Hopi hairstyles were definitely considered for Padme in TPM, and the idea that Lucas "always wanted them" (where have I heard that before?) probably comes from that point in time. But as far as Leia goes, it was pretty clearly Flash Gordon all the way as the principal (if perhaps not only) influence.