A further point to Q2.
IMHO.. The constant chord design lends itself better to the adjustment of trim tabs. Remember the whole idea is equal lift along the blade length (as much as possible, however it is almost impossible) but also equal lift generated from all of the blades. To do this each blade needs to be tuned as you are probably well aware, therefore in a blade with a twist, you are essentially fine tuning the twist, and in a blade which was designed to be twisted, this will create very little additional stress loading. I would think a blade designed to be flat would have problems... raising the point that if you had a variable chord, designed to be twisted.. whats the point??? I would suggest twisted blades give the designer an easier ballpark to play in to achieve equality of lift.
PPS