Replace your trigger spring when you replace your recoil spring. You probably don't need to, but the spring is so cheap, and the replacement so easy, that there's no good reason to take the chance. Not like on a Beretta 92, (that trigger spring is a pain) but I digress. I don't know the official, factory-recommended interval for replacing the Glock recoil spring. The 9mm could probably go 4,000 or more rounds, though I assume that the heavier calibers would be harder on springs. You can just test it. With the trigger depressed, point the muzzle straight up, and very gently allow the slide to close on an empty chamber. If it closes all the way, your recoil spring is fine. If it doesn't, then you need a new recoil spring. When the Glock is "cocked" it isn't really cocked. It's about 1/3 cocked.
I don't see any benefit to rotating magazines. A magazine spring is not like a pitcher's arm; it doesn't regain strength after a few days of rest. When it takes a set, it takes a set. Use it as intended, and when it falls out of spec, replace it.