Μετά το πρωινό είμαι χορτάτος για αρκετές ώρες.

In Greek, the verb form often already tells you who the subject is.
Here, είμαι means I am, so the pronoun εγώ is not necessary.

• είμαι = I am
• εγώ είμαι = I am too, but with extra emphasis

So Greek often leaves out subject pronouns unless the speaker wants contrast or emphasis.

Μετά means after here. When Greek μετά means after, it is followed by the accusative case.

So:

• μετά το πρωινό = after breakfast
• μετά το μάθημα = after the lesson
• μετά τη δουλειά = after work

That is why you see το πρωινό and not a nominative form.

Greek uses the definite article much more often than English. So where English says after breakfast, Greek naturally says after the breakfast in form:

• το πρωινό = breakfast

Even though it literally contains the, you should usually translate the whole phrase naturally into English, not word for word.

Πρωινό is a noun meaning breakfast. It comes from a word related to morning.

In this sentence:

• το πρωινό = breakfast

It is neuter singular, which is why the article is το.

Χορτάτος means full, well-fed, or satisfied from eating. It usually refers to food, not just a general emotional kind of satisfaction.

So in this sentence, it means the speaker is not hungry after breakfast.

A useful contrast:

• χορτάτος = full from food
• γεμάτος = full in a more general sense, like a full glass, full bag, full room

Greek learners often notice that χορτάτος is specifically about having eaten enough.

Because χορτάτος is an adjective, and it must agree with the person it describes in gender and number.

Here, χορτάτος is:

• masculine singular

So this sentence sounds like it is spoken by a man.

Other possible forms:

• χορτάτη = feminine singular
• χορτάτο = neuter singular

So a woman would normally say:

• Μετά το πρωινό είμαι χορτάτη για αρκετές ώρες.

Greek commonly uses είμαι + adjective to describe a state.

So:

• είμαι χορτάτος = I am full

This describes the result or condition. If you wanted to talk about becoming full, Greek could use a different structure, but here the sentence is simply describing the speaker’s state after breakfast.

It means for several hours.
Here, για is used to express duration of time.

So:

• για = for
• αρκετές = several / quite a few
• ώρες = hours

Together:

• για αρκετές ώρες = for several hours

Because αρκετές is an adjective meaning several or enough / quite a few, and it must agree with ώρες.

• ώρες is feminine plural
• so the adjective must also be feminine plural
• therefore: αρκετές

Compare:

• αρκετός χρόνος = enough time / plenty of time
• αρκετή δουλειά = enough work / quite a lot of work
• αρκετές ώρες = several hours

Because the phrase means for several hours, so Greek uses the plural noun ώρες.

• η ώρα = hour
• οι ώρες = hours

Since αρκετές means more than one, the noun must be plural too.

Not completely. Greek word order is more flexible than English word order, although some versions sound more natural than others.

The original sentence:

• Μετά το πρωινό είμαι χορτάτος για αρκετές ώρες.

You could also hear:

• Είμαι χορτάτος για αρκετές ώρες μετά το πρωινό.

Both are understandable. The original version puts Μετά το πρωινό first, which gives a natural time frame at the beginning: After breakfast...

Not in the same way.
If you want to say after breakfast, the normal choice is μετά.

• μετά το πρωινό = after breakfast

Από usually means from, so it would change the meaning or sound unnatural if substituted directly here.

Yes, it is natural and understandable. It sounds like a normal everyday sentence.

A Greek speaker might also say similar things such as:

• Μετά το πρωινό δεν πεινάω για αρκετές ώρες.
  = After breakfast I’m not hungry for several hours.

• Το πρωινό με κρατάει χορτάτο για αρκετές ώρες.
  = Breakfast keeps me full for several hours.

But your original sentence is perfectly normal.

Only the adjective would change:

• Μετά το πρωινό είμαι χορτάτη για αρκετές ώρες.

That is because χορτάτη is the feminine singular form.

Everything else stays the same.