Okay, somewhat old-ish thread, but hey, I'll post my two cents anyway.
From a Tibetan perspective, the Buddhist teaching (dharma) is a ladder, composed of three steps;
1) Theravana or Souther Buddhist tradition, which is mostly concerned with liberating an individual. This is sometimes in the West seen as the 'essence' of or 'original' Buddhism, as per our obsession with age (the older it is, the more original it must be, and originality is good).
2) Mahayana or Northern Buddhist tradition, which is concerned with grasping two spiritual concepts; 'emptiness' and 'lovingkindness' or 'compassion', and cultivating a 'boddhichitta' consciousness instead of the 'arhat' consciousness of the Southern Tradition..
3) Vajrayana or Tibetan Buddhism, which is concerned with becoming a Buddha through meditation, yoga and adequate grasp of the two, from this perspective, 'preliminary' steps.
Mahayana tradition is in general more accepting of women and homosexuality. However, the Western idea of Buddhism being a sort of 'If it harms none, do as thou wilt' of the East in what comes to issues of sexuality is often somewhat wishful thinking. I understand the thorough disappointment with Western patriarchal monotheist traditions which fuels this search for a more accepting tradition, but there is no religion on Earth which is free from prejudice or can be totally harmonized with our personal understanding of sexuality.
That being said, I feel that the Vajrayana Tradition is perhaps most accessible to Westerners who seek to transform desire and positive self-image into spiritual tools. Buddhist concerns of non-duality and interbeingness speak to profoundly feminist concerns, as well. However, polyamory coming from a language of 'needs' isn't really coherent with Buddhism in my mind. The point in most Eastern esoteric traditions is realizing that the Experience, the Experiencer and the Experienced are one and the same. Thus I seek to become free of addictions in the form of 'needs' and 'wants' instead of constantly looking for new partners to feed into them.
Me: bi female in my twenties