How tight should I tighten the bar nuts on a chainsaw?

Hand-tighten with the wrench until snug, then give it another quarter turn. That’s close enough to the 15–25 ft-lbs most saws specify. A torque wrench is overkill here — the bar has to move slightly when you adjust chain tension later anyway. Overtighten and you risk stripping threads in the housing; undertighten and the bar wanders.