1999 Honda Accord Going downhill

You probably won't hurt anything but while the brakes are designed to slow a car going down a steep hill, coasting in a lower gear adds to internal engine wear and can promote oil getting sucked up past the piston rings, and burned. Regardless, you don't want the engine to run faster than what the manufacturers recommends. If you have a tach on the dash, you'll see the numbers in red that you mustn't exceed.

As far as wear, I can help you replace worn brake pads when the time comes. You won't be doing your own engine work if that becomes necessary. Brake pads and rotors are fairly inexpensive so don't worry about wearing them out.