This is my first time attempting modding. I've read the Humanoid Races 2.0 wiki but it still doesn't really help me. I have no idea how to make it so psychite tea is completely poisonous to them, I have no idea how to make it so the only have three finger and two toes. I know what they would look like but don't know how I would be able to restrict them to have the thin body model (They look similar to humans) and I don't know how to make it so they need to wear a specific suit in order to survive for a while. I know exactly how the suit would look like but also don't know how I would be able to graphically implement it. HELP!
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You could try to look at the xml definitions that another working race has, to begin with.
If you want them to have a unique anatomy, you need a new BodyDef.