Has it been shown he has out and out slaves?
Off hand; don't know.
I know from reading the odd comic here and there his society is intensely stratified.
With it going from primitive tribal, to dirt floor and bricks on up to uber-techtopia for the elite.
This of course may vary somewhat from writer to writer but still.
Black Panther may straight out have slaves or maybe simply the bottom level of his society should count as slaves anyways, do the manual labor, live in huts with no access to wealth or resources, have to do exactly what Black Panther says.
If they aren't slaves, pretty close to it.
You know by comparison.....Dr. Doom doesn't have some kind of primitive vikings or 15th century people living in his kingdom....
Maybe not him personally, but African tribes routinely enslaved (members of) tribes they defeated in battle. Wakanda is probably as isolated as it is because it enslaved and absorbed all neighboring tribes early in its history.
I wouldn't be surprised, it certainly claimed a large portion of one of the largest water sources nearby. I'm actually surprised they managed to remain isolated after all those years but then they pretty much straight up killed any body who approached them didn't they?
Not sure about that, seeing as they thrived in secret for so long. They likely avoided outside devil contact/kept the slaves for themselves.
Probably; don't see them degrading themselves by interacting with the mercantile system of other cultures. That and honestly; what did any one else have to even other them for most of existence?
I mean, aside from the Eternals or some other secret high techno-society also hanging out somewhere?