Decided to consolidate dwarves and gnomes into one race, in my setting. They're redundant with each other; Paracelsus, who came up with gnomes as his earth "elementals", also called them pygmaeus—what that means to a Swiss German is left as an exercise for the student. Also as is pointed out in the TV Tropes article OurGnomesAreWeirder, the gnome in D&D is the dwarf from European folklore, the dwarf is the dwarf from Tolkien (usually via Warhammer, I would add). This also gives me a roughly human-sized "fairy" humanoid and a small one, like humans and halflings, without trying to wedge in the "human sized but weirdly proportioned" fifth wheel.
Decided to give them dwarf magic resistance (6 + HD), energy resistance 5 to both fire and acid, 120 ft. darkvision, and stonecunning, and the spell-like abilities I'd previously given dwarves, but also gnomes' ability score adjustments, obsessive trait, and keen senses. They have dwarves' weapon familiarity (hammers not axes, handguns, firearms are martial weapons), but use both the gnomes' mushrooms (particularly for armor) and the dwarves volcanic-pool algae (particularly for weapons). The rationale of that is that, while elves' gods are both the one tree, the dwarves' gods are fire and earth, two things that are more separate. Also dwarves make more stuff (although I guess this kinda makes the dwarves a lichen, a super rare rhodophyte-basidiomycete one). Maybe the dwarves can also make their algae weapons into the copper that harms neutral-aligned outsiders.
Decided they use largely dwarven language, which has the interesting effect of making all four of my protagonist cultures (elves, dwarves, inland Númenor, hydrocratic Púkel-men), except for halflings (who are an offshoot of the thalassocratic Valyrians), use a language inspired by Tolkien. I decided to take out plural forms and aspect distinctions in the verbal stems that both nouns and inflected verbs derive from, and just have three main verb paradigms: active/agent focus, passive/patient focus, middle/intransitive (in Austronesian alignment the important question is which noun that relates to the verb is in the direct case and which in the oblique one, and intransitive verbs only have a direct-case noun). Still haven't figured out which of their alphabets they'll use, Dwarven or Gnomish.
The gnomes were from the planet, but the dwarves that I consolidated gnomes into (and vice-versa) still come from one of the moons, which means I might have humanity have just grown up naturally, on the planet, unobserved by the more advanced lunar races because you can't see cavemen from orbit.
Not sure what to do about their coloration. Probably yellow structural coloring, in their skin, with phycoerythrin turning them various shades of orange, red, or pink. I thought I might have to give up on white dwarves and purple-haired gnomes but there are rhodophyte algae in basically every shade of red and magenta, up to dark lavender-violet with no red at all.
I struggled with what to do with orcs and ogres, if they should all be much bigger than their dwarf ancestors, but I hit on this: female orcs are gnome-sized (male and female gnomes are the same size), then male orcs are as much bigger than them as male mandrills are compared to females. Then female ogres are the same size as male orcs, and male ogres are mandrill male-to-female larger than them. This gives me Small orc females (whose stats become +2 to Strength and Dexterity and -2 to all mental stats), Medium male orcs and female ogres (which latter have the stats of orcs), and Large male ogres.
