VDC is nothing but slicing the chasis to different line cards.
you no need to worry admin vDC that is for management.
Are you looking each VDC different nexus 9300 ? and vPC
Make a small chart and port config, Migration approach port by port.
you need to look as below :
Look at Layer 2 vDC - to Layer2 config in nexus 9300 acting as layer2
Look at Layer 3 vDC - to Layer3 config in nexus 9300 acting as layer3