Your on the right track. VDC off for tracking. I did leave mine on when we had a soaked trackday.
If the tarmac is shinny from the rain be cautious VDC on. If the tarmac is grey from slight rain I take it off and ease into the sission until I feel comfotable.
Then to add one more deminsion you can do the YAW sensor mod to have zero traction control.
just make sure your comfortable with the traction of the car before you cut out VDC or YAW