to seize this opportunity? You had asked yourself once, but do you have an answer? Your action so far seems to be natual defensive bahavior. It is like if another girl approachs your boyfriends you would fight feicely to win him back, even if you wouldn't care much about him otherwise.
From what what you descibed, it is a very demanding position. It is also several levels above what you are. What he had warned you about standing up for yourself facing people more senior than you, is a very valid question. It is not as easy as you had said. Even if you win every battle, it still would take a toll on your health, your family life...
It is a very rare opportunity. It will definitely jump start your career - I mean, post-baby post-greencard stage career. However, his evaluation for you is pretty acurate. He needs somebody that he can use. If he choose you, you he would have to put time into mentoring you (I assumed this from your posts). It is not you are not intelligent enough, but, there is somethings you learn only from experiencing it. You will need 100% dedication, willingness to sacrifice everything, real full support from you boss, and full support from you hu*****and to succeed. Are you ready for it?
I admire you that you delivered yourself very well, you kept objectiveness in all your narative. You are very honest to yourself. I didn't read any pretentiousness anywere. You are a great person, and a very intelligent and capable girl. What I wrote was by no means any advice. It is just my two cents in evaluating your situation. From reading what you wrote, my guts feeling is that, you boss will make the right decsion...may it be you or not you.