The UltraTab class has a Reposition() method, which seems to be what you're looking for to move tabs.
While I don't see a single property that contains how many rows are being displayed, there is a RowNumber property off the UltraTab class. You may be able to loop through all tabs in the VisibleTabs collection of the UltraTabControl, and determine how many unique RowNumber properties you see. Take a look at the API documentation for the UltraTabControl.IsMultiRow property (link leads to online help documentation for NetAdvantage for .NET 2008 Volume 3) for an example of looping through the VisibleTabs collection and inspecting properties on individual tabs.
I don't see any "minimum tabs per row" property. You may want to submit a feature request to have such a property implemented in a future release of the toolset.