I'm planning on starting with Isabela, no competition. Then whoever is the male bisexual LI (reeeeeally hoping for Fenris, just because I love characters who used to be enslaved/tortured/experimented on) will get some mHawke loving. I prefer to choose the s/s option whenever I can, even if it means I won't be playing my own gender, simply because I identify more with the idea of a homosexual relationship than with the heterosexual one.
I'm really hoping Merill will be bi too, then she'll go before the male bi char, but if not, then she'll be the third (I'll just make a very androgynous Hawke and pretend he's genderqueer).
I'm still not sure about Anders. I loved him in Awakening but the abomination thing is just... Well, we'll see. After seeing the game I think I'll be able to tell if I want to go there with him.
On the subject of incest, (I know it's semi-closed but I can't resist): relationships with siblings/any member of your close family are never equal. There is a power imbalance which is impossible to deny. There is "omg I can't lose my sibling/parent/other relative forever so I have to keep up the relationship even if maybe I don't want to" issue. There's other messy psychological stuff. At best, it's dubious consent. At worst, it's statutory rape. In any case, the 'two consenting adults' argument is on shaky ground, if it even stands at all. All the other stuff, like legal issues and the social stigma attached to it, I believe were mentioned, and were declared not enough of an argument.