Dear (name witheld),
As-salaamu 'ala man ittaba'a al-huda (peace be upon those who follow the true guidance). I was delighted to learn of your serious consideration and possible intention to accept the Islamic religion. No doubt that step would be the greatest thing in the entire NN years of your life. This step is the one that will protect you from the everlasting punishment of Hell and open to you the path to Heaven after death and will result in success and happiness in this life and the hereafter. I advise you to hasten with your decision and do not hesitate and postpone. You seem to me to be of sound wisdom that will lead you the path of truth by the will of God (Allaah).
As for your first question, it is permissible in the Islamic religion for a Muslim to marry a woman from the People of the Book (Christain or Jew) if she is chaste (i.e. of high moral character) and virtuous, as Allaah has stated in the noble Qur'aan (interpretation of the meaning of verse number 5 in the chapter entitled "Al-Maa'ida," The Table):
"This day are (all) things Good and pure made lawful unto you. The food of the People of the Book is lawful unto you and yours is lawful unto them. (Lawful unto you in marriage) are (not only) chaste women who are believers, but chaste women among the People of the Book, revealed before your time, when you give them their due dowers, and desire chastity, not lewdness, nor secret intrigues (girlfriends or lovers)..."
Based on this verse, your marriage contract will remain valid if you accept Islaam and become a Muslim, and it will not require renewal. Your remaining with your current wife is permissible as long as she is virtuous and chaste in marriage.
As for your second question, the child in Islamic law must follow the Muslim among his or her parents, and it is the Muslim parent's right and responsibility to ensure his or her proper upbringing, guidance, and supervision. Your statement that you would seek to expose your children to Islaam is a wise and judicious foresight. And we hope that with the passing of time that they will be convinced of this religion and implement it in their lives.
No doubt that you will face some difficulty in convincing your wife to raise your children in the Islamic religion considering the promise you have made to her. However, the use of wisdom and gentle judgment will aid you, God willing, in overcoming this difficulty. This is important especially considering that it is expected that you will exert a concentrated effort in inviting your wife to Islam, since if she accepts it, the problem will be solved from its roots.
In any case, and no matter what the results, the first step towards success will be your accepting the religion of Islaam yourself. We pray to God (Allaah) the Almighty and Magnificent that He eases your affairs and brings you success in finding the path of truth and that he guides your entire famliy to Islam.
I would be more than happy to dicuss any other questions or concerns you may have. Salaam. Peace.