best to set to 0. less strain on wrench

If there are no instructions in the pack to leave the torque wrench at a specified setting then it may be left in any setting you require. This item is best left in a clean and slightly oiled (with a good oil spray) condition. I would advise you to wind the setting to the minium setting as this will relieve any pressure on the torque mechanism and enhance the life of this valueable torque wrench..

best to leave it on the lowest setting when in storage so nothing is streched over time

yes

Every bolt or screw has a certain torque limit. If you exceed this limit you may end up damaging the bolt or screw or worse still, the bolt or screw may break. To answer your question, rather increase the torque wrench setting by a small margine at a time. Your chances of damaging the torque wrench will then be nil as you may cause damage by applying more force after the click. Do not exceed the maximum setting of the torque, rather use a spanner. The main function of a torque wrench is to ensure that the bolt or screw you are tightening is done to a specified torque setting.

both