Kate, I don't understand your gripe with Artaxerxes becoming king in 465 BCE and sending Nehemiah away to build Jerusalem's walls a few years later. He became king in 465 BCE and in his 20th year he sent Nehemiah to rebuild the walls. That brings one to 445 BCE, give or take a few months. This date corresponds to the calculations done by Hoehner and Feinberg.
Few historians question the authenticity of the book Nehemiah/Ezra, originally one book. Some of the edicts contained in Ezra were written in Aramaic and are viewed as originals. So whether you calculate the 70 weeks as lunar or solar years, you still come out to Jesus' ministry and death. This is what Paul Tanner had to say about Dan. 9:
Daniel 9:24-27 is “a glorious messianic revelation of the Lord Jesus Christ, announcing among other things the time of His coming and His death before the cataclysmic events of A.D. 70. The passage remains a bedrock of prophetic revelation.”1
Tanner reviewed the literature, especially the Church Fathers, even that of Jewish scholars, and this was his conclusion:
Yet from the literature that is available some vital conclusions can be drawn. All the early church fathers, along with Jewish scholars, interpreted each “week” as a period of seven years and applied this quite literally (though Origen took the final week as seventy years, i.e., a week of decades rather than years). Significantly, of the eleven early church fathers surveyed in this study all but one of them held to some form of messianic interpretation of Daniel’s prophecy (the lone exception being Hilarianus who held to a fulfillment in the time of Antiochus IV Epiphanes in the second century B.C.).2
1. J. Paul Tanner, “Is Daniel’s Seventy-Weeks Prophecy Messianic? Part 2” Bibliotheca Sacra Vol. 166 (July 3009): p. 339. Dallas, TX: Dallas Theological Seminary.
2. J. Paul Tanner, “Is Daniel’s Seventy-Weeks Prophecy Messianic? Part 1” Bibliotheca Sacra Vol. 166 (April–June 2009): p. 198. Dallas, TX: Dallas Theological Seminary.
But of course it's your choice what you want to believe. Bart Ehrman concentrates on NT textual criticism, which is negative and subjective to the extreme. If you do not supplement it with some objectivity and historical reality, your faith will be destroyed in no time. That means you have to allow for the benefit of the doubt until such time as something is proved wrong. At least Ehrman believes that Jesus did exist, but not as what he is portayed in the NT. But where do you draw the line?