That sounds like a good itinerary. One day devoted to the National Park &
USS Cairo with next day devoted to Grand Gulf, Port Gibson & Raymond.
On Saturday, I would recommend taking Hwy 61 down to Port Gibson/Grand Gulf (
be sure to try to see the Windsor ruins while you're in the Port Gibson area).
After that, I would recommend taking the Natchez Trace Parkway up to Raymond.
It's about thirty five miles at 50 mph, but well worth it. There's historic & natural sites along the way with a good chance of seeing much wildlife. It's a very therapeutic drive . . . unless there's a bicycle marathon underway.
No must sees or must eats along that portion of I-20, that I can recommend.
I would suggest going on to Vicksburg and using that time in Park/
USS Cairo.
Although the Vicksburg NMP is much smaller than others,
Gettysburg for example. It's also been called one of the nation's greatest "art parks". Many monuments, statues, ect.
In other words, there's a lot to see in a compact area.