As I thought, the welts of this pants took as much time as the rest of the construction. It took me 1 1/2 hour. The result is this, with the welts still held together with a zigzag stitch:
For the construction I mainly used the method described by Ann Steeves (Gorgeous Things) in a Threads article last year. I think you can find it on her blog as well (but you have to search, I can't find it right now).
As for the pants itself, here are some pictures of how it is without waistband still. Lining has to be added too.
The front and waist are OK, only the back has folds, I hope they disappear when I add the waistband and pull up the center back a few millimeters.
Anyone any idea how to get those folds away?