- IME, the plan does not make sense. Water heaters don't last forever, and usually when they start leaking it's time to think really hard about replacing them before the leak gets worse. "Plumbers tape" is not likely going to get you very far. If the leak is due to corrosion of a thin flexible tube ("metal hose") it may fall all the way apart when you attempt to remove it, necessitating an emergency call to a professional, a quick trip to the hardware store, or doing without hot water for a while. At least make sure that you time your operation when the hardware store will be open.
1a. - if you've misidentified a flexible electrical conduit as a metal hose, it could get even more exciting. Though hopefully not if you've turned it off first.
Two. Turn off the water heater. Run hot water from any/all hot taps until it's not hot. Turn off the cold water supply to the hot water heater. Leave a hot tap open (water should stop coming out when you turn off the cold supply to the hot water heater - leaving it open serves as a vent to allow air in when you drain the heater) Use the drain on the bottom of the hot water heater to drain it. You might be amazed at what comes out the drain at first ;-)
If all goes well, remember to refill the water heater (close the drain, leave the hot water tap open, open the cold supply valve, wait until air stops coming out the hot water tap, close the hot water tap, and check for leaks) BEFORE you turn the water heater back on. If it's turned on while full of air rather than water, it's not good...