Sorry I took so long to get signed on and welcome you, but welcome, welcome to our forum. I can see from your post that you have many concerns to work out, and I just want to say that if you take things slowly, and communicate a lot with your partner, it will help.
As far as poly being balanced, I just want to point out that it doesn't always have to be. My own poly family is a case in point, we are a V with two "arm" partners and one "hinge" partner. The hinge has a romantic relationship with both arms, but the arms just have a platonic relationship with each other. Therefore, we are "unbalanced" -- it is uneven which of us has two partners and which has one (or one-half, if you want to get mathematical).
But we are okay with that. There's plenty of love to go around, and we have a life that works for us. I think that polyamory opens up a wide, wide world, of many configurations, with all kinds of geometry. That's just diversity, and it's not always a bad thing.
The most important thing is to find out what works for you and your partner. Lots of checking up with her about how she is feeling about things will probably help a lot; it will give you an idea which directions can handle some more "pushing," and which need some easing off.
Remember, too, that people's thoughts and feelings can change little by little over time. For example, your partner might find hetero sex to be a little freaky, but if she's exposed to it just by small degrees, she may find that she has a tolerance for it (even if it's not something she'd want to do herself).
I hope Polyamory.com can be of some help to you as you seek to sort things out. Again, sorry for the lateness of my welcome, but it's sincere and respectful and so I hope it will do.
Love means never having to say, "Put down that meat cleaver!"