I really dig being able to unlock cosmetic customization options, but “Man’ari Eredar” seem a bit extreme for just “cosmetics”. The Draenei are a very distinctive culture, and it definitely does not overlap with the Eredar of Argus.
Now first off, I would suggest using the name “Eredar” for them. “Man’ari” is a term that refers very specifically to the most vile of the Eredar, which is why I would reserve the name to only refer to “evil Eredar” moving forward.
For cosmetics, you honestly could just port over most of those options you gave to the Draenei. I might have an onyx-black skin tone as well, just because I think it would mesh well. They obviously have some Fel and Void themed visuals, maybe more of an orange/fiery color for their eyes as well.
I would change their tails, though, to give them longer, slithering tails. Nothing crazy or anything, just enough for a bit of visual distinction. I would also probably add a “true black” hair color. Maybe some monotone grey skin colors as well, mirroring Archimonde a bit, but overall sticking more towards red hues.
Maybe a couple “bald” variations with various “plates” or horns as well. You gotta squeeze a Diablo reference in there somewhere.
Now, where I would shake things up is that for Classes, they obviously don’t get access to Paladins (and probably not Shamans, given Nobundo was the first). I would add the ability to become Demon Hunters if possible, however, as I think they would probably fit the class well, both visually and thematically. I would add Orcs as a parallel for the Horde, as well.
As far as Racials go, I’m not really sure. A fun idea (although perhaps broken) would be the ability to “bribe” hostile NPC’s/enemies to turn them yellow to you, kind of referencing how for most of Warcraft history, they would deceive other races into allowing them into their midst. Would be mechanically pretty useful in a lot of situations as well, just trying to run past certain mobs, stuff like that (obviously, disabled in any sort of competitive environment like BG’s, Raids, or M+).
Otherwise, I would dig some of the “cracked” skins the NPC’s in Legion had, red skin with bright fel-green energy showing through. Maybe something sort of Void-themed as well, and maybe also something more broadly just “Arcane” in nature (the Eredar were originally all exceptional Mages, as I remember), just so they don’t feel totally shoehorned into being “evil”.
For my part, I think a good Horde counterpart to the Eredar would be formally adding the Grimtotem Tauren, but with more “spooky” visual options. Eerie face and body paint designs, splintered looking horns or antlers (looking more like branches of a dead tree), maybe even faintly glowing eyes (being touched with some form of dark magic), and maybe less polished-looking hooves.
Anyways, just my take.