Ek is nog nie gereed om te vertrek nie.

Afrikaans normally uses double negation in full clauses.

• The first nie appears where the negation starts or is attached to the item being negated.
• The second nie usually comes near the end of the clause.

So in this sentence:

• nog nie = not yet
• final nie = closes the negative sentence

That is why you get:

• Ek is nog nie gereed om te vertrek nie.

A simpler comparison:

• Ek is gereed. = I am ready.
• Ek is nie gereed nie. = I am not ready.
• Ek is nog nie gereed nie. = I am not ready yet.

Here, nog means still / yet, and together with nie it gives the meaning not yet.

So:

• nog on its own can mean still, yet, or sometimes another/more, depending on context.
• nog nie is a very common combination meaning not yet.

Examples:

• Ek slaap nog. = I am still sleeping.
• Ek is nog hier. = I am still here.
• Ek is nog nie gereed nie. = I am not ready yet.

Because nog nie is the normal fixed order in Afrikaans for not yet.

So you say:

• Ek is nog nie gereed nie.

not:

• Ek is nie nog gereed nie.

To an English speaker, it may help to think of nog nie as one unit meaning not yet.

Gereed is an adjective, meaning ready.

In this sentence it comes after is and works as a predicate adjective:

• Ek is gereed. = I am ready.

Afrikaans adjectives used after verbs like is do not change form. So gereed stays gereed.

Om te vertrek is the infinitive construction, meaning to leave / to depart.

• vertrek = leave, depart
• om te vertrek = to leave, to depart

After words like gereed (ready), Afrikaans often uses om te + verb:

• Ek is gereed om te begin. = I am ready to begin.
• Sy is gereed om te praat. = She is ready to speak.
• Ons is gereed om te vertrek. = We are ready to leave.

So in your sentence, gereed om te vertrek means ready to leave.

Yes. That would mean:

• Ek is nog nie gereed nie. = I am not ready yet.

Adding om te vertrek makes it more specific:

• Ek is nog nie gereed om te vertrek nie. = I am not ready to leave yet.

So the shorter sentence is natural if the context already makes clear what the person is not ready for.

Vertrek means to depart / to leave, and it is a bit more specific than gaan.

• gaan = go
• vertrek = leave/depart

So:

• Ek is gereed om te gaan. = I am ready to go.
• Ek is gereed om te vertrek. = I am ready to leave/depart.

Vertrek can sound a little more formal or more focused on the act of leaving from a place.

In this sentence, the first nie is part of nog nie.

So the order is:

• Ek is nog nie gereed ... nie

If you remove nog, then the negation looks like this:

• Ek is nie gereed nie.

So the position of the first nie depends on what is being negated and what adverbs are present. With nog, the normal combination is nog nie.

In standard Afrikaans, yes, in a full negative main clause like this, the final nie is normally required.

So:

• Ek is nog nie gereed om te vertrek nie. ✓

Without the final nie, the sentence sounds incomplete or non-standard:

• Ek is nog nie gereed om te vertrek. ✗

There are a few special cases elsewhere in the language, but for a learner, the safe rule is:

• if the sentence is negative, expect the closing nie.

Yes. In natural English, both are possible depending on context:

• I am not ready to leave yet.
• I am still not ready to leave.

Afrikaans nog nie can overlap with both of those ideas. In many everyday contexts, not yet is the most direct translation.

Then you would use nie meer ... nie, not nog nie ... nie.

• Ek is nie meer gereed om te vertrek nie.

Compare:

• nog nie = not yet
• nie meer = no longer / not anymore

So these are very different:

• Ek is nog nie gereed om te vertrek nie. = I am not ready to leave yet.
• Ek is nie meer gereed om te vertrek nie. = I am no longer ready to leave.

Yes:

• Ek = I
• is = am
• nog nie = not yet
• gereed = ready
• om te vertrek = to leave / to depart
• nie = final negative marker

So the structure is:

• Ek
• is
• nog nie
• gereed
• om te vertrek
• nie

That is a very typical Afrikaans sentence pattern for this kind of negative statement.