So played a bit today. And jotted down some more stuff.
1: I never used the sawmill mod before, but 20 planks per 1 log? Isn't that a bit much? Of note is that the skill uses carpentry of course, and the plank reaction causes the koa to level up in carpentry at a very high rate. Completing 1 plank reaction is like 20 carpenter actions. Try changing your reaction to produce 1000 planks and use a no-skill Koa to do it. You'll get an insta-legendary. xP
2: The reactions to produce mana gems from your normal turnips returns no normal turnip seeds. I suppose that could be a way to keep turnips as a rare commodity, especially since the only way to get seeds from them is to let the koas eat them raw.
3: The mana gem reactions appear to be working as intended. Of note is, mana gems can be cut and encrusted. Perhaps giving them a value can be nice too, so you can use them as a decent decoration source.
4: Books.... Currently seems to have no use for them except as very low value trade goods, considering the 3 leathers and 3 jobs to make one. I suppose the value on it would've been better had I used something better than a dabbling leather worker. But right now, I'd see most people just sticking with their standard uses for leather. Perhaps making books required for the building of the mana furnace and altars would work, as well as make them into reagents with a small chance of being used up in mana reactions. Also if you've ever seen the display case mod, you can do something like that with books. Take 2 blocks and 3 to 5 books or something and build them into a reactionless 1x1 workshop as decoration and call it a bookcase. Could be the Koa equivalent of statues everywhere.
Well I be done for now, if I notice any other oddities or come up with a good Koa idea, I'll let ya know.
Edit: Was thinking since the koas seem to be developing towards a wood based economy vs the usual dwarven stone ones, I'd write a little reaction for them that I may use on the next fort.
[REACTION:MAKE_WOODEN_MECHANISM]
[NAME:make wooden mechanisms]
[BUILDING:CRAFTSMAN:CUSTOM_M]
[REAGENT:logs:1:WOOD:NONE:NONE:NONE]
[PRODUCT:100:1:TRAPPARTS:NONE:GET_MATERIAL_FROM_REAGENT:logs:NONE]
[SKILL:MECHANICS]
Wooden mechanisms for the Koas.