Anyway, yeah. The bolded cannot be emphasized enough.Depends how low Econ goes, but generally its a 1:1 exchange between Econ and Centralization.
More Fishing, Farms (Step or Regular), or Pasture land should keep things stable. However, given the military necessities, investing in the military is probably a good idea, even if it will be disruptive.
Also, the expedition won't necessarily chase the nomads out onto the plains, it is just that you are compelled to fight it out. Failure to pay back the attack this turn is unlikely to cause problems, but the score needs to be settled in some way eventually.
Investing in war carts is a good idea even after factoring potential short term starvation risks. Word of AN.
We will be compelled to attack until we get our pound of flesh. If this turn's war party doesn't do satisfactory damage, next turn it's likely that War Party will be locked in as Main. We are not able to hunker down and let them break upon our defenses as long as Eye for an Eye is not satisfied