Water heater supply lines

I have a gas water heater and would like to replace the two flexible copper supply lines at the top of tank. I was wondering what I should do in advance of removing the supply lines to minimize the amount of water I'll have to deal with when I remove the lines to replace them. There is a cutoff valve for one of the lines and there's an expansion tank just beyond the connection for the other line.
Basically, my quesitons are these:
Do I need to turn off both the main water to the house and the cutoff at the top of the tank, or just one of them?
Do I need to drain the tank either partially or fully before removing the lines?
Do I need to worry about the pressure release valve?
Any tips you might provide would be greatly appreciated, including anything I should know when I turn the water back on after replacing the lines.
Thanks in advance for your help.
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Sgana333 wrote:

Try turning the one at the tank inlet. Verify that it closes by opening hot water taps. If you get more than a dribble, you'll have to shut the Main.

Turn the gas off or at least set the control to "PILOT". With the water shut off and Hot taps open, drain some water from the drain cock on the tank bottom. It will take a few bucketfuls to get all the water out of the piping. As a test, open the relief valve; if no water comes out, you've drained enough to get the level in the tank below the top of the tank.

Not specially.

Leave the Hot taps open as you (slowly) open the supply valve. This will let the air out. When you get all the air out, fully open the valve and turn the gas control back on. Inspect the work for leaks:-) Jim

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Jim,
Thanks for the great direction! It's very much appreciated.
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