Congratulations and I’m sure you’ll have a grand time in Africa.
I do the flight across five times a year, sometimes via Europe, sometimes straight. There is nothing that’s gonna make it great, but acceptable is the goal.
It comes often down to the mindset. It will pass, it will be fine, we’ll have a grand time, don’t sweat the small stuff. All those things works.
Delta usually has some OK movie selection, but a couple of movies on your pad may help out.
Perhaps some Africana related books to read on your pad as well.
Try to sleep, drink water, walk around every so often to minimize the swelling that will undoubtedly be worse by sitting still.
Overnighting in Johannesburg is a grand idea before the flight to PE, gives you more peace of mind to make the connection, with or without going through with rifles etc.
I have at times taken muscle relaxants to ease some of the pain, which may work for some.
A noise cancelling setup, Bose or others is worth a lot, both to get the rest and to drown out the noice when watching a movie or listening to music.
Just in case you do get jet lag, I usually get it bad on the Eastbound trips, have some sleep aid or Melatonin. You can get them easy in Atlanta at the pharmacies, but not so easy in South Africa.
You’ll be fine.
//Gus