Running my homebrew CoW (Pathfinder-flavor) each weekend.
I kept humans out of it, for the most part at first, since that was a big thing that was a part of the 2.0 version. When I did this, I ended up replacing them with orcs (in the absence of the more clever humans I figured orcs would expand into the vacuum). So, any modules that I run, generally have re-writes to replace humans with orcs.
Humans are generally planned as barbarians (or seen that way even if they are civilized), and/or are fugitives living beyond the law (hidden settlements).
I started with the three main races broken out in the 2.0 version as the core for the dragon's companions (elf, dwarf, gnome). But have allowed for more variety as time has gone by.
But as far as the rest of it goes, I have been expanding things as it made sense to.
Have placed the dragon area on a different plane, to be honest; with semi-permanent 'hidden' ways to get back and forth from Golarion. But with that weakening, have added in a bunch of meddlesome fey, and demons/devils - since the plane's barriers are thin.
My 'had to be human' player, got shipwrecked on Fireshore Island. Noticed that there was a big part up north that was not claimed. Decided that was 'wilderness or frontier' with orc settlements here and there. Grabbed about four modules I had never run and wove the area from a blend of them.
As it lucked out, one of my modules was about a quasi-roman ancient (and dead and gone) civilization which meshed very nicely with the dragon culling of the humans. The other was about an undead 'king' and army. Then you have the CoW dragon council stuff (running them as a higher nobility on standard fiefdom structure). I try to keep 3-5 threads open to let them choose their next path.
I have the dragon + companion group, and two other non-dragon groups (half-dragons and dragon disciples, but no true dragons here). The Council people show up very infrequently for that second group, and are always there for the first.
There is a big push from the Golarion gods making in-roads for the non-dragon races; with missionaries found in different areas.
Since the Red Dragon's are into slavery in the 2.0 edition, I ruled that *any* race could come from them - and in fact there is a clan that is interbreeding with all kinds of races intentionally trying to breed a master 'companion' race - but don't tell my players that just yet. :-) As for the other dragons, I look at their favored terrain, and then look at the humanoids and monsters from that terrain. When you start to match up general temperaments and outlooks that are complimentary you get a few that really stand-out.
Anyway, good luck to you!