I replaced the one on my YJ last winter and I’m running the stock amperage one. It only really matters if you’re running lots of accessories like lights, winches, air compressors, a big stereo system. Changing it wasn’t difficult, the worst part was loosening the tension on the belt. There’s two or three bolts that have to be loosened on the power steering pump bracket and there’s a long bolt on the fender side of the pump that sets the tension. As for starting it, it should be fine. The cooling system is full of water, so that helps keep it from getting hot, but best not to run it for longer than you have to.
Joe