Popular as in how populous? There is a handful of them played habitually. There isn't a specific half-orc grouping for them. There's a slew of factions on Amia, and probably can find a fit there somewhere for virtually every concept.
Orcs and their subbreeds aren't very popular from a 'how many of these are there' standpoint. We have a fairly decent halfling population, but there are some abberations on Amia. I would be wary of cutting teeth and taking Cordor specificly as the 'Amian' experience. Amia allows for people of all familiarity levels with RP, and tries to make it a home where all levels of capability are at least enabled to have fun. Cordor is a lot like Sigil.. just with more half/lesserbreeds and other things, due to the tolerance policy/trade city.
Custom PRCs/Races get no bonus stats, You can request one which is not on the subrace page on the lefthand side, and attempt to find what of the existing Subraces best fit it. ...However it'd probably require a skin change which you will need Dream Coins for, which are rewards for excellent RP. Which you can't get till after you've been RPing.
I'd get a feel of the server with something a bit more friendly. Its a pretty huge module.
Just so you're aware, if you -do- decide to do a grey-orc later, you will have to make a request and it will have to be a completely new PC, its just the way things are done.
Amia's DM staff is pretty evenhanded about the requests but custom race PC's usually are something which they attempt to dissuade people from playing for their first PC on Amia. (Part of it is also them getting to know you as a player from seeing what you do from the client.)
