Is it permissible to marry a divorced Orthodox Christian woman, with an agreement on Islamic conditions, or is it a condition that she embrace Islam first?

It is permissible for a man to marry a chaste woman from the People of the Book, but it is preferable to marry a righteous Muslim woman, due to the Sharia (definition)-based precautions involved. If she embraces Islam, then your marriage to her is good, based on the hadith (definition): "We have not seen for two who love each other anything like marriage." It is permissible to invite her to Islam, and it is better for a woman to invite her to avoid fitnah (temptation/discord). It is not advisable to marry her until she embraces Islam, due to the risks involved for the husband and the children.