All in all pretty plausible theories. But hopefully we are in for a few surprises as well.
If I've understood the lore correctly, New Amsterdam is more independent than the rest of America in this timeline. Sort of like Hong Kong before Chinese takeover. And being more independent should serve Tara's purposes since it is likely easier to influence politicians in the city than in the country.
When talking to Tara about Mom in the salon, Tara is very well aware of Mom's raging libido at least. The question is if Tara has some deeper plan or if she just wants to have fun.
Maybe Viv's dad just was someone Tara needs to impregnate women so all those lovely lesbians can be born.
Viv definitely dated guys in the past. The game doesn't say much about how long lived those relationships were. Mostly says she has had several boyfriends, she usually don't have sex with them for a few dates and all previous boyfriends were lousy at cunnilingus.
I don't think just sex appeal / awakened sexuality is enough to explain Ms Harper's interest in Vivian. Especially not on the dom route. It's like Viv suddenly commands a presence that wasn't there before.
Also remember that Mom has lusted after Vivian long before Tara kissed Viv. So there are other things in play as well.