This is an excellent topic. Like you said, we're often brought up learning a romantic or idealized vision of Greece, where Roman debauchery tends to be more out in the open (although the fetishization of imperialism still never seems to end). It's great to see people challenging that by examining some of the more unsavory, sobering realities of Greek life. You've picked up on a lot of the important things to keep in mind when approaching slavery in antiquity. There are key differences from American slavery, but it's nevertheless extremely dehumanizing. Being conquered often meant large-scale enslavement of survivors, as in Melos, the Sicilian Expedition, etc. And you're correct that in Athens, one didn't go around whaling on slaves in public because it was hard to distinguish status by appearance.
If you haven't already, you may be interested in looking into helots, a large proportion of Peloponnesians enslaved (and ritually humiliated and mistreated) by Sparta — there were so many that controlling them to prevent rebellion was one of Sparta's most chief concerns. You could also check out Athens' policies on citizenship for more info on the disenfranchisement of slaves, manumission (freed slaves shared a social status with metics, Athens' "resident aliens"), and other issues.
I'm glad to hear that you've gained some independence yourself. I can relate, and I hope you're doing well now. This is a thoughtful examination of a complex issue, and I'm really looking forward to what you make during the jam!