The Dodge Caravan has a Cd of 0.35
I found it here -->
Vehicle coefficient of drag specs - Mechanical Database
It is entirely possible to drop your drag by over 50%. It depends on how far you want to take your modifications
I do not know of a cylinder deactivation kit. That is a pretty drastic mod that could result in catastrophic failure. Focus upon the proverbial "low hanging fruit*" first, then reach for the stars
*Air dams, grill blocks, increased tire pressure