This is the main thing, in my opinion. Therapy isn't needed to have this realization.

Therapy can help, and it would be over time, in addressing the vestiges of your upbringing that might disrupt the practical aspects of raising children. But it seems that you do have time for therapy to help with that, seeing as it will in fact take some time to actually have children to raise. And please keep in mind that it is not only children who grow and mature; their parents can as well.

Well this is a broad question and might merit its own thread. My thoughts are that compatibility is useful first in the sense that you just like to be with one another, you enjoy each other's presence. Second, it is useful in being able to articulate compatible visions for how children are to raised. Recall that compatible is not the same as identical.

This strikes me as an unrealistic expectation, as you mentioned. There is little certainty in life, and here you have just been with her a few months. You are just beginning to grapple seriously with these questions with her in mind. I think it is okay to have some doubts at the moment, and to discuss things honestly with this woman with whom, you say, childrearing would work if it is going to work with anyone. I think that doubts will lessen over time, as the right decision, whatever it may be, becomes clearer to you through discussion and reflection.