May the support order be stated in terms of the percentage, and thus vary as the paying parent's income varies?

No. The statute requires that the amount be calculated based upon the guidelines and other factors, but the support order must be for a definite dollar amount. This causes problems when the supporting parent is self-employed, or his or her income is variable, but since a child support is a judgment, and to facilitate collection and enforcement by state authorities, the legislature has determined that a percentage order will not be valid.