However, if he plead guilty to a felony, he could have been sentenced to as many as 5 years, despite the government's agreement not to argue for me. Each additional conviction would increase the cap by 5 years, though the guidelines calculation would remain the same. No wonder he didn't want to plead to 13 felonies.
Technically, this is correct, since federal sentencing laws limit the judge's discretion to raise or lower prison sentences. They actually have a table indexed by "points" which the judge must use to determine the length of the sentence. Thus, in order for the prosecution to honor a plea for 6-7 months, it would necessarily have entailed that all of the (other) charges either be dropped or reduced to their misdemeanor equivalents. (Note that if you read her CV, she hasn't handled a case in the federal courts since the sentencing guidelines were issued.)