Depending on the context and the expression, il faut has several translations : one need, one must, one should, it is required, it is suitable, it takes, …

In all of your examples, falloir might be translated by "require":

Il ne faut pas y aller. → It is not required/allowed to go there.

Il ne faut pas longtemps pour y aller. → It doesn’t require a lot of time to go there.

Il n’en faut pas moins que vous y alliez. → "*It doesn’t requires less than you going there", it really means: You should go there anyway.

Il ne me faut pas y aller toute suite. → It is not required for me to go there right away.

The third sentence is tricky because it is a set expression. Unlike the others, you cannot remove the negation and keep a meaningful sentence:

"Il en faut moins que vous y alliez" would not be understood nowadays.

TL;DR : when applied to a noun, the positive form expresses a need while the negative form indicates the absence of need. When applied to a verb, the positive indicates an obligation while the negative expresses an interdiction. Make sure the negation is applied to falloir and not to another part of the sentence.

You’re right, in this particular case “pas” is applied to “moins“. “Pas moins que” and “rien de moins que” are used for emphasis ; both translate as “nothing less than”, but you could remove them without really affecting the meaning. Your translation is totally correct.

The same applies to your 3rd example : “n’en… pas moins” basically means “still”. The negation is applied to “moins” : what follows is “not less valid” despite whatever “en” designates.

In your 4th example, your translation is wrong : “il ne me faut pas…” could be rephrased as “il ne faut pas que je…” : “il ne me faut pas y aller seule” = “il ne faut pas que j’y aille seule” = “I mustn’t / shouldn’t go alone”. Actually, while “il me faut [verb]” is common, “il ne me faut pas [verb]” isn’t ; your original sentence feels odd.

You need to make the difference between verbs and nouns, just like when using the positive form : in most cases, “il ne faut pas [verb]” means “one mustn’t…” while “il ne faut pas [noun]” means “one doesn’t need…”. When one wishes to express the absence of obligation instead of an interdiction, another phrasing should be used like “il n’est pas nécessaire de“. You can compare this to English : “must not” is unambiguously an interdiction while “don’t have to” means it’s not required.