Estou prestes a começar o rascunho da redação, mas ainda não escolhi o tema.

Estou prestes a means I am about to or I’m on the verge of doing something.

It is a very common structure in Portuguese:

• estou prestes a sair = I’m about to leave
• ela está prestes a chorar = she’s about to cry
• estamos prestes a começar = we’re about to begin

In your sentence, Estou prestes a começar... means the speaker is very close to starting.

Because estar is used for a temporary state or condition, while ser is used for more permanent identity or characteristics.

Here, being about to start is a temporary situation, so Portuguese uses estar:

• estou prestes a começar = I am about to start

Using sou prestes would sound wrong.

This follows the usual Portuguese pattern:

• estou cansado = I’m tired
• estou pronto = I’m ready
• estou atrasado = I’m late

These are temporary states, so estar is the correct verb.

Because prestes is normally followed by a + infinitive when you say someone is about to do something.

So the pattern is:

• estar prestes a + infinitive

Examples:

• estou prestes a sair
• ele está prestes a ligar
• estamos prestes a começar

English speakers sometimes want to translate word-for-word and guess something like prestes de, but that is not the normal structure here. The standard form is prestes a.

Rascunho means draft or rough draft.
Redação here means a written composition, especially something like a school essay.

So o rascunho da redação is:

• the draft of the essay/composition
• literally: the rough version of the writing assignment

A useful distinction:

• rascunho = the preliminary version
• redação = the piece of writing itself

So the person is not just starting to write; they are starting the draft of the piece.

In Brazilian Portuguese, redação is very common in school and exam contexts to mean a composition, essay, or writing assignment.

For example, Brazilian students often say:

• tenho que fazer uma redação
• a redação do ENEM
• o tema da redação

Ensaio exists, but it usually refers more specifically to an essay in a literary or academic sense, and it is less common in everyday school-style phrasing than redação.

So in this sentence, redação sounds very natural if the context is a school assignment, exam essay, or composition exercise.

Because da is the contraction of de + a:

• de + a = da

The noun redação is feminine singular, so with the definite article it becomes a redação.

Then:

• o rascunho da redação
  = the draft of the essay

This is the same pattern you see in many Portuguese noun combinations:

• a porta da casa = the door of the house
• o título do livro = the title of the book
• o fim da aula = the end of the class

So da redação is just standard contracted Portuguese.

Because escolhi is the preterite form of escolher and here it means I chose. With ainda não, it often corresponds to English I still haven’t chosen.

So:

• ainda não escolhi o tema
  literally: I didn’t choose the topic yet
  natural English: I still haven’t chosen the topic

Portuguese very often uses the simple past where English prefers the present perfect.

Compare:

• Ainda não comi. = I still haven’t eaten.
• Ainda não terminei. = I still haven’t finished.
• Ainda não decidi. = I still haven’t decided.

So even though escolhi looks like simple past, in this context it naturally expresses an action that has not happened up to now.

Not with the same meaning.

Ainda não escolhi o tema means:

• I still haven’t chosen the topic

But ainda não escolho o tema would sound unnatural here, because the present tense escolho suggests a habitual action or an action happening now, and that does not fit the idea of not having made the choice yet.

If you want the meaning in the sentence, ainda não escolhi is the natural choice.

Because Portuguese often omits subject pronouns when the verb form already makes the subject clear.

• Estou already tells you the subject is I
• Escolhi also clearly means I chose

So Estou prestes a começar... is perfectly natural without eu.

You could say:

• Eu estou prestes a começar o rascunho da redação...

but the eu is usually only added for emphasis, contrast, or clarity.

For example:

• Eu estou prestes a começar, mas ele ainda nem chegou.

Here eu adds contrast: I am about to start, but he has not even arrived yet.

Portuguese often uses definite articles more than English does.

So escolhi o tema literally means I chose the topic, but in English we might also say I chose a topic depending on context.

In Portuguese, if the speaker has in mind the topic for that specific essay, o tema is very natural:

• a redação = the essay/composition
• o tema = the topic/theme for that essay

This makes the sentence sound specific and complete.

They are related, but not always identical.

• tema = theme/topic, especially for an essay, discussion, or artistic work
• assunto = subject matter, matter, issue, what something is about
• tópico = topic, but often sounds a bit more formal or structured, like a listed discussion point

In a school writing context, tema is the most natural choice:

• escolher o tema da redação = choose the essay topic

You might also hear assunto, but tema fits especially well with redação.

Yes, it is understandable and natural enough, though there are a few other common ways to say similar things.

Your sentence says:

• começar o rascunho da redação = start the draft of the essay

Other natural possibilities include:

• começar a redação = start the essay
• fazer o rascunho da redação = make/write the draft of the essay
• começar a fazer o rascunho da redação = start making the draft of the essay

So the original sentence is fine. It emphasizes that the person is specifically starting the draft stage.

It creates a contrast:

• Estou prestes a começar o rascunho da redação = I’m about to start the draft
• mas ainda não escolhi o tema = but I still haven’t chosen the topic

So the speaker is pointing out something slightly contradictory or problematic: they are about to begin, but they are missing an important step.

The word ainda means still in this context, and mas means but. Together they make the second half feel very natural and conversational.

A little, yes, but the original word order is very natural.

Original:

• Estou prestes a começar o rascunho da redação, mas ainda não escolhi o tema.

Possible variation:

• Estou prestes a começar o rascunho da redação, mas não escolhi o tema ainda.

This also works, but ainda não escolhi often sounds a bit smoother and more standard than não escolhi... ainda.

So while Portuguese allows some flexibility, the original order is a very good model to learn.

Yes, mainly the word redação in this context.

In Brazil, redação is extremely common for school compositions and exam essays. A Brazilian learner will hear phrases like:

• tirar nota boa na redação
• fazer a redação
• o tema da redação
• corrigir a redação

So even though the grammar is generally standard Portuguese, the overall phrasing sounds very natural in Brazilian educational contexts.