Well, this is the best anyone has done so far! :-)
Your explanation is that Mary understood that she would undergo a virginal conception, and just wanted to know the mechanism. If she had simply said, "how can this thing be?", then this would be a much stronger argument. She goes on to say, though, "since I know not a man." At the risk of sounding like a broken record, why would she add that phrase if she knew that there would not (and could not) be a man involved in the conception of the Messiah?
I think you misunderstand my fundamental goal here. I am not attempting to argue, based sola scriptura, that the Orthodox belief is correct. I don't think that such a thing would be possible. All that we can maintain is that our beliefs regarding the Theotokos are consistent with Scripture, properly understood. I don't expect you to be convinced even by that, but I acknowledge that it is the very best I would be able to do on a Protestant playing field.
What happened was that I saw monkfan ask a pretty straightforward question -- one that the Orthodox account has a ready answer for. We understand that since Mary had taken a vow before God to remain a virgin and felt called to be a virgin, this announcement by an angel seemed to be placing something holy (a life of virginity in order to be devoted to prayer) in opposition to something holy (bearing a holy child.)
We also understand that she knew that Satan can appear as "an angel of light," and that it is possible to be deceived. We understand that Eve's fundamental mistake was that she did not question the serpent when he said something contradicted what God had told her. Thus, she made bold to question the angel, in order to be certain that she was not being deceived in the same way that Eve was -- we see a direct parallel between these events. Once the angel had answered her definitively and she understood that there was no contradiction, then there were no more questions -- only acquiescence to God's will. We do not see her as being "curious" in the least -- if mere curiosity as to mechanism were the motivation, one would expect that she would have had many more questions for the angel as to details.
I then observed that monkfan wasn't getting a straight answer, and as he points out, if we are going to have these discussions, the playing field has to be "even." Thus I interjected myself. (You are equally free to call us on the carpet when we engage in speculation that isn't supported by our own tradition and standards of faith!)
If Protestants are going to categorically and unequivocally state that the Orthodox belief that at the time of the Annunciation Mary was planning to remain a virgin, is not and cannot be true, and if you are going to state that your absolute certainty on this matter is based on Scripture alone, then you have to have a very good explanation for this particular passage. And so far, I'm still not convinced that you have made an argument that would meet your own standards.
It matches your beliefs, but it doesn't meet your standards of Scriptural proof. I'm perfectly content if you wish simply to say "we Protestants have as a dogma the belief that Mary never intended to be remain a virgin, and thus we have to read that verse in the light of our belief." :-)
Actually, I think my argument is far stronger than yours-but what would you expect me to say. :O) If we were to suppose Mary included the, "How can this thing be because I am a virgin?" as you suggest, I would say this is no different than the doubting Zachariah statement of how can his wife give birth. Both would be claiming doubt about how God could do a particular thing. But the response from the angel is far different in Zachariah's case than in Mary's case for we know the angel made Zachariah dumb where with Mary he simply answered her question.
This can only mean Mary was not asking it as a question concerning God's ability. With your interpretation such doubts exist with Mary's statement. With my interpretation Mary is not questioning the Lord but simply asking how something is going to transpirer.
I can't argue with your other interpretations of Mary simply because they are not part of the inspired word of God. They are based upon traditions handed down. Some of those traditions may be valid. Some may be fanciful. But few if any is recorded in scripture.
As Full Court argued, you will have a far more difficult time arguing with Matt 1:25 than I have with Luke 1:34. There are other places that seems to indicate Mary had other children.