Not sure about the first three questions but the QRH is the Boeing approved procedure. If receiving an EICAS message ‘Flaps/Slats Disagree’, you are required to complete the appropriate checklist from the QRH as there maybe a very good reason why the Flaps/Slats failed to reach the selected position in the required time. Why complicate things keep it simple if you can, only my opinion of course. Most companies require that from after engine start to engine shut down you comply with any EICAS message and complete the required QRH checklist!
If on the ground and you select the flap handle to a take off flap position and it is not seated correctly in the detent you will receive a flap disagree message. On the 757 (the 757s I used to operate)you needed to reset the PDUs (alternate switches need to be recycled) but on the 767 you only need to position the flap lever in the detent to remove the message, if my memory serves me correctly.