the slave thing is somewhat perplexing as some parts of ape land seem to have slaves while other parts seem more like servants or squatters or something.
Yeah, that was one of the problems with the series. Some humans are slaves, some are peasant farmers but under ape control, some humans seem to do whatever they want. Alan and Pete seem to freely be able to walk around the countryside. They should have at least been consistent with humans legal status.
They never really made it clear what type of economic system they lived under.
It's possible that the individual Prefects have some flexibility over the rules to be governed in the lands they control. But areas such as the fishing village could be so remote that no Prefect is involved, any ape can take charge over unattended humans, apparently.
It feels like they're modeling the series to be similar to the post reconstruction U.S. South.
I don't think they put a lot of thought into the socio economic dynamic of humans because this was basically a show targeted to kids.