It usually tells you on the box. All lights are different, it depends on the wattage.
Most of these lights tell you how many can be attached to one another. That is the guideline for getting them all to light up. You will not likely blow a fuse from string lights.
Yep, usually stated in the box or tag on the lights. Generally no more than five strings.
Thanks to everyone....didn't think to look on the box.