Hi!
To answer your questions...
1. It does'nt matter much if the wing is set a little positive to the stabilizer (higher at the leading edge).
2. It does matter! If you have the wing twisted so the tip of the wing is flying at a more positive angle than the rest of the wing that means disaster!!!!! It means that the wing will stall easily and that the plane will turn in that direction.So if you have a plane that at take off immediately turns to the right or snap rolls esily , it means the left wing-tip is warped (twisted wrong, with the leading edge flying at a more positive angle than the trailing edge). All wing tips should be twisted slightly negative, that means that the tip should fly at slightly negative angle than the rest of the wing.
No measurement is needed doing this just heat the plastic film on the wing and twist it slightly!