From the perspective of an artist and a worldbuilder, I feel it would be best to keep the number of races to a minimum in in Masterwork Reborn.
For starters, keeping the number of races to a mimimum would make Masterwork DF more approachable for newbies. Goblins and Orcs are very similar races, for instance, so newbies might find it difficult to remember which race has which traits. Also, if you keep keep the number of new races low, you'll have a lot more diversity. If you wanted a race to drive other creatures insane, for instance, you'd be better off attributing that to Clowns instead of creating an entirely new race to have that trait. Any traits that couldn't be attributed to existing races will go into new ones, which means you'll be playing a VERY different game depending on what mode you play.
Lastly, if you avoid adding too many new races, it'll be much less of a load for artists. Every new race you add will add 198+ new profession graphics, which means things will become exponentially more time-consuming the more races you add. Just look at the
S'Lanter. They had to be cut from Fallout because adding a new race would be too much of a burden for the artists. Adding new content to existing races, on the other hand, will expand the gameplay without increasing the graphical load. The amount of tiles in Vanilla DF is already mind-boggling. I've finished retexturing projects for NetHack, Minecraft and Earthbound Zero, but DF proved so enormous that it's the only cancelled project I've ever had to date (DwarfFortress).
So with that being said, I think you should limit yourself to only two new races (along with the existing Dwarves, Humans, Elves, Goblins, Clowns and Kobolds). An avian race and an aquatic race would work just fine for the new ones. We already have enough races based off of earth, fire and nature so enough of those!
TL;DR:
KISSOh, interesting! I checked out the other thread, your artwork is really nice. I saw you were working on an orc model there. I'd be happy to give your new tileset a spin if you do get around to making one.
Orcs, like goblins, are every shade of green, or occasionally ash grey. Their eyes are several shades of deep red.
Oh, and I almost forgot to thank you! From a clarity perspective, I think it would make a lot of sense for orcs to be gray because goblins are already green. Thanks for the thorough response!