I agree with jaiswalamrita on this. The negation would be to change "Do Not" to "Do" because they are logical opposites.
For your related questions:
1-None is not the opposite of most. In some cases, you could use "least" as the opposite of "most". The most profitable method v. the least profitable method. For this sentence, there really isn't an opposite to most.
2-To negate the sentence you only change one item because otherwise you get a double negative, which is no change at all.
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