If you are storing the pistol loaded, it must be that you want it to be ready for immediate use. That being the case, I'd have at least the magazine fully loaded.
Springs do not fail because they are stored under stress. They fail primarily by fatigue (being cycled). Even so, a well designed and properly heat treated spring has a fairly long life. Springs are inexpensive and their periodic replacement is as much a normal maintenance item as is cleaning the mag itself.
As to the safety position and possible stresses on springs, that probably depends upon the model. I'd leave the safety "off" unless the chamber were loaded. The first thing you are going to do in a defensive situation with an unloaded chamber is to rack the slide and probably reposition the safety to "on". Having to place the safety "off" first is just another thing to do in a potentially stressful situation ... and you don't need that any more than you need a half-loaded mag.