Just jumping in here... Is there a way to link to the webinar that you are mentioning? Or is it a private thing?
Recording to the "CAD/GIS Integration and Workflows" webinar can be found here: Esri Department of Transportation Webinar Series
Create a CAD file Directory, inside create a folder for each projected zone in your state. Then take the ".prj" files for each zone and place them in the corresponding folder. Rename the file esri_cad.prj. For example in Ohio there are 2 state plane zones. Ohio Stateplane NAD 83 North and Ohio Stateplane NAD 83 South I’ve attached a zip file with an example of how the folders should be organized. Then place the CAD files that correspond to each zone in their proper zone folder.