Well Kat that depends what we're defining as early tribal religion. I've looked into many african traditional religions which are the first religions and I found a wider variation from sky father creators, to the universe being created by a married couple of deities, to creation by a hermaphroditic deity. In native American religions, it is clear that the feminine is deeply important. However I found just many father deities as creatrixes. However you are right in that the grandmother spider deity is a common figure who appears in the mythologies of the Navajo, Zuni, and Pueblo peoples. I have also heard that in the mythology if the Australian Aborigines that the creator was a mother Goddess. The Koreans have one as well. It's a shame its harder to find more information on Korean Shamanism. I've been fascinated ever since I saw a filmed Shaman's rite. I have also heard of some south american religions where a Goddess seems to take primacy. In polynesian lore I found married mother and father deities as well legends where no one deity created the universe. The Hawaiians in particular had no creator deity. I will concede that since the growth of sedentary society is linked to war, that the importance, equality, and reverence of the Goddesses may have been diminished as people began worshipping male Gods of battle more fervently. I'm not saying that there ware no female war deities as mythology would prove me incredibly wrong, but as you said, the male sky deities tend to be linked to battle. I am not skeptical of a time when the great Goddess was afforded as much respect as her consort, but I am skeptical of the particular slant of the matriarchal prehistory theory because of what I know about some of these cultures. However, I have seen religions whose prime deity is a great Goddess so I will not doubt the existence of such religions in ancient times and that there are likely Goddess oriented religions that may have been lost to time as a result of certain events.
As for your Questions tmso:
I plan on fleshing out the society first then writing even though I have a sort of Game of Thrones (for lack of a better novel to compare it to) style plot. I don't want to give too much away as I have not planned out everything nor do I want to spoil it.
Men have opportunities though if one looked at my notes on sex and courtship, one might assume men are no more than walking phallic organs. However men are allowed other opportunities. Most government positions however are off limits to them. There are loop holes, but everything has to be just so. The intellect of a man is not doubted, so much as his ability to channel his thoughts or to remain coherent in their expression. While men are not thought of as blithering idiots, they are considered impulsive. Part of a man's courtship of a woman is that he has to prove himself a valuable asset to not only his potential wife, but her family's elder crones.
As for third sex groups, this is a very complex issue, the handling of which I drew from historical sources such as the two spirit groups of Native American societies, a peculiar Indonesian tribe, and more contemporary studies with a dash of my own imagining. "Effeminate" men experience a sort of privilege that normal men do not. They are divided into two groups, one which is considered to be male, but to have the touch of a Goddess, and what our society would describe as heterosexual. They are considered men, but for the most part are afforded the same respect as a woman. They marry women, they can do what one might call "men's" work in this society, and their word outside of the bedroom carries the same weight as a woman, and unlike other men the value of said word increases at the same rate with age. However the second group of "effeminate" men which are what we would call homosexual are outright considered women (whether they think of themselves that way or not). The treatment of homosexuality is a very complex thing, and most men do not consider these persons viable sexual partners as they cannot become pregnant nor are they really interested. Furthermore a male engaging in homosexual acts who is not a part of this second division is often scorned because he is seen as denying his spouse her children(since everyone ends up married one way or another), specifically her potential female heirs. In another way, it is result of the man having the audacity to think he can take a woman's role. Remember, more "masculine" gay men in this society are not considered women. The other half of the group IS considered female and thus are not shunned for these activities. This society is both very strangely homophobic towards gay men and in some ways oddly accepting. One might think it would be as simple as allowing for an affair if a woman's husband is gay and was a part of an arranged marriage, however, this is considered adultery and thus frowned upon, and just about any man who can breed is married to a woman. I haven't gotten around to female third sex groups, but I'll probably be working that out soon. I imagine a female equivalent comprised of more masculine women would hold less stigma with the way this society treats lesbianism.