Can you use Bruges as a base to explore the Flemish country and World War I history. Four days too much?
I stayed in Brugge for 3 nights and loved it. I only took one tour out of town. I hope I can go back someday it is truely lovely, historical and a must see. so well preserved!
If you were going to spend four days in Bruges without leaving, I would say it is probably too much. To use it as a base to explore the surrounding area, four days should be fine.
Depends on what exactly you wanted to see in the countryside. If for WWI history you meant the Ypres (Ieper) Saliant, Kortrijk would be a better base, but Bruges would work as well. But you'll need a rental car.
If you want to see a huge collection of WWI (and WWII) material, visit the Royal Military Museum in Brussels.