What is the best treatment for a torn rotator cuff?

It depends. Many people have degenerative rotator cuff tears as we mature. Non operative conservative treatment should be the first line of treatment. This often consists of NSAIDS, injection, and physical therapy. If conservative treatment fails or if an acute traumatic tear, operative treatment may be warranted. Ask your orthopaedic surgeon for more details. Good luck.
Depends on degree. Of tear and also your level of activity and expectations. If it is a complete tear, you may need surgery. If you can lift your arm out (laterally, abducted) above 90degrees, most likely not full thickness tear. If its not full thickness, physical therapy, strenghtening and ergonomic/work changes can benefit. Do not immobilize your shoulder as it can lead to frozen shoulder.