125 views and no replies... I feel compelled to throw you a bone, I know its hard work coming up with this stuff.
Well I like the theme of the race, we already have the germans as a military race, but this takes the theme in the same direction but with a different advantage. I think the issue for me is that I find the military victory to be one of the easier victories to achieve early, in particular with 4 or more players where people are guarding their borders from several angles and are usually not that willing to send troops to defend another Civ and leave themselves open for someone else to steal a military victory. Still the ability is just a notch up from a wonder (hanging gardens If memory serves me correctly) where you gain 1 plastic at the start of each round.
Their is a kind of self balancing aspect to this, in that you can only have so much plastic at the table so this race recovers faster than other races from the lost of plastic, but I find in most games sometime midway through everyone has all their plastic on the table and given that they don't actually have any kind of combat advantage it would depend on what the great person Shaka looks like. If he is like Napolean I think this would make the Zulu tough.
Its hard to call it from just reading the race, I think it will probobly require some play testing and adjustments to their racial tile to even things out. I mean a race like this with a big production advantage in their home tile would make them even more prone to military victories.
You might want to consider slavery as a different ability all together. Perhaps simply give them the Hanging Gardens ability.
Nice effort regardless, let us know how the playtesting goes.