I wasn't actually thinking "tree hugging elitists elves", I was thinking more "non-agressive humble creatures that prefer to keep to themselves and avoid conflict". Self-defense bloodshed would be pretty difficult to avoid in the game, but to incentivize players to use non-lethal methods, maybe they would be very physically weak and have piss poor armor and no weapons. Maybe, if possible, they'd get very bad thoughts from seeing any kind of carnage at all. I don't know if temper tantrums are hard-coded, but if possible, if they stay too long in the "miserable" state they could get that "depressed" state that a civ member gets when they fail to make an artifact (yet another incentive to avoid bloodshed; too much of it would make people in your fort just wither and die).
To survive invasions, one could perhaps use pylons that release a gas with a syndrome that makes any hostile invader become peaceful or just leave (don't know how feasible this is to program; maybe make them "vanish", saying that the pylons transported them to their homes?). These pylons could be more mid to late game, requiring energy and rarer materials.
To avoid early sieges, other than traditional walls perhaps the creatures would be able to build early temples where a prayer would send the attacking force away, the rate of success depending on how skilled the creature praying is at spellcraft. Maybe the creatures themselves would be able to inflict syndromes that make the affected enemies fall sleep, so as to buy time for the spellcaster to invoke the "send invaders away" spell sucessfully.
I would make them have NOEAT, so they wouldn't need to hunt and harm animals. The only sustenance they'd need would be drinks (maybe make them alcohol dependant so they have to farm for something else other than cloth). I'd make them at peace with wildlife too, to avoid problems with agressive animals.
What else.... maybe they can't dig very well (like kobolds), but they have workshops that allow them to synthesize gems and a special block material (as strong as, say, granite) for crafting and building walls. Farming could actually be used for this; certain plants can be synthesized into certain gems, which in turn fuel their magic. A nice 3-stage industry.
Maybe there could be a very late game workshop that can turn invasions on and off, like a giant cloakng spell or something (basically an actual "win" condition for them, which would take a looot of effort to achieve).
Pets would be all about milking and shearing. No hunt or war trainable, of course.
As for WHAT, exactly, this race could be, physically wise, I was thinking on just making a monster up. Some small, physically frail beings. I'm a big fan of non-traditional designs for sentient races (see my own creature raw in my signature, for instance), so I'd like to make them weird looking. As I wrote this I kinda envisioned them as having white, thin, tailed and hunched humanoid bodies with digitigrade feet, long arms and hands, and large
diplocaulus heads. Maybe the size of kobolds or slightly larger/smaller.
...you know, I'm actually kinda fond of this idea. I might try my hand at doing something like them one of these days, if you'd rather go another route with your own race.