Here's something I discovered. Since I hate to hard-code anything, I found out the right equation to get the number of resources that I want for Horse Whispering -- 2 Horses on Small or smaller, 3 Horses on Standard up to Huge, and 4 on Giant or Gigantic -- turned out to be number of default players divided by 9, plus 2. Anything less of a denominator and I get too many required sources on Gigantic.
Also, I was slightly concerned about the game crashing if I fed a text string too many arguments. With X as the default number of players for the world size, Horse Whispering is going to require X/2, rounded up, Stables, and 2+(X/9), rounded down, Horses. So on Standard you need 5 Stables and 3 Horses. The help text for quests relies on calculating the required values in Python and then feeding those values into the text string. I can't do anything about the non-English text strings, so if we add a second quest requirement, the current help text won't be able to show that, but at least the text manager doesn't care about a second number hanging out doing nothing.