1)2) We've never mentioned these issues before, so you'll have to rely on Vilage, Aaron's or Gorgenmast's Word of God.
3) Generally, a depression is characterized by low investment, low consumption, high unemployment, etc. You can try to stimulate the economy by lowering the interest rates to encourage borrowing, and hence investment, you can decree an increase in wages, but be careful of all the unwanted consequences, the State can employ people for public works to stimulate consumption...
4) If by collapse you mean a return to anarchy, that would seem excessive. Even during the chaos of the French Revolution, the French economy never blew up completely. During the actual WWI, French GDP fell 24%. In the PoW timeline, with a war dragging on for 12/3 years, a 50% fall wouldn't be excessive. That would be an incredible fall, but if the government managed it decently, at least maintaining basic services, the country should have retained the ability to rebound after the war. Keep in mind that huge destruction also means huge opportunity to rebuild and stimulate the economy.

Honestly, I don't think the depression would have occurred in the 30's, if at all, due to the severe disturbances wrought upon the world economy by the war. Admitting economic history followed in PoW a similar path as in real life, the depression would have hit in 1940 or later.