No, it is not necessary to talk about all the details of your experiences for them to be processed.
Yes, you may. Emotions and sensations may come up during processing; although, you will be prepared and your therapist will help you safely manage them. Once they are processed, they rarely come back!
No. During EMDR processing, you are present and fully in control.
EMDR, as with all treatment approaches, will help you accomplish your treatment goals. The length of time that it takes is dependent upon the complexity of your problems. Frequently, EMDR is only one of several treatment approaches that will be used to help you reach your treatment goals.