No, you do not need a master ball, if you get it to a low enough hp, you can catch it with an ultra ball. You can find mew in the end of the cave in cerulean.
no it won't be holding a master ball cos when you used the master ball to catch a certain Pokemon, the master ball will be gone in your inventory because it is a consumable.
No.
After you defeat Giovanni in Sliph Co. the President will give you the MASTER BALL.
no
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