Eu como iogurte com cereal e torrada no café da manhã.

Yes. In Brazilian Portuguese, subject pronouns are often omitted because the verb ending already shows who the subject is.

• como = I eat
• so (eu) como is understood either way

Including eu can sound:

• more explicit
• more contrastive, as in Eu como iogurte, mas ele come ovos
• more natural in some contexts where you want clarity or emphasis

So both are correct:

• Eu como iogurte com cereal e torrada no café da manhã.
• Como iogurte com cereal e torrada no café da manhã.

Yes — como can be different things depending on context.

In this sentence, como is the 1st person singular present of comer:

• eu como = I eat

But como can also mean:

• how
• as
• like

Examples:

• Como você está? = How are you?
• Trabalho como professor. = I work as a teacher.

In your sentence, because como comes after eu and before food words, it is clearly the verb to eat.

Not necessarily. In Portuguese, when talking about food in a general way — especially what you usually eat — it is very common to use the noun without an article.

So this sounds natural:

• Eu como iogurte com cereal e torrada no café da manhã.

You might use articles if you mean something specific:

• Eu como o iogurte que comprei ontem. = a specific yogurt
• Eu como a torrada que você fez. = a specific toast

So in your sentence, the lack of articles is normal and natural.

Grammatically, it can look a little ambiguous, but in normal interpretation it usually means:

• yogurt with cereal
• and toast as another breakfast item

In other words, people will usually understand:

• iogurte com cereal
• e torrada

If you want to make it extra clear, you could say:

• Eu como iogurte com cereal e uma torrada no café da manhã.
• Eu como iogurte com cereal e também torrada no café da manhã.

So the original sentence is fine, but it has a small natural ambiguity that context usually solves.

Because no is a contraction:

• em + o = no

The expression is:

• o café da manhã = breakfast

So:

• em o café da manhã becomes no café da manhã

This contraction is required in normal Portuguese.

Also, inside café da manhã, you have:

• da = de + a

That happens because:

• manhã is feminine
• so de a manhã becomes da manhã

So the full structure is:

• no café da manhã = at breakfast / for breakfast

Because café da manhã is the fixed expression for breakfast in Brazilian Portuguese.

It is not being built word by word in a completely free way; it is just the normal name of the meal.

Compare:

• café da manhã = breakfast
• almoço = lunch
• jantar = dinner

So even though de manhã means in the morning, the meal itself is called café da manhã.

They are related, but not the same.

• no café da manhã = at breakfast / for breakfast
• de manhã = in the morning

Examples:

• Eu como pão no café da manhã. = I eat bread for breakfast.
• Eu estudo de manhã. = I study in the morning.

So if you say:

• Eu como iogurte de manhã

that means I eat yogurt in the morning, which is broader.

If you say:

• Eu como iogurte no café da manhã

that specifically means I eat yogurt at breakfast.

Portuguese handles this a bit differently.

Torrada is often treated as a countable item:

• uma torrada = one piece of toast / one toast item
• duas torradas = two pieces of toast

In a food list, singular can sound general or represent the item as part of the meal:

• iogurte com cereal e torrada

If you want to emphasize more than one piece, you could say:

• iogurte com cereal e torradas

So the singular here is acceptable, but plural may also be natural depending on what you want to express.

Sometimes, but como is the safest choice for regular yogurt eaten with a spoon.

In Brazilian Portuguese:

• comer iogurte is very normal for spoonable yogurt
• tomar or beber iogurte can be used more easily for drinkable yogurt

So:

• Eu como iogurte = very natural for standard yogurt
• Eu tomo iogurte = possible, especially if it is liquid/drinkable

Since your sentence has iogurte com cereal, como is especially natural.

Yes. Portuguese allows some flexibility.

Your original sentence is neutral and natural:

• Eu como iogurte com cereal e torrada no café da manhã.

You could also say:

• No café da manhã, eu como iogurte com cereal e torrada.

That version puts more focus on breakfast as the topic.

And if you drop the pronoun:

• No café da manhã, como iogurte com cereal e torrada.

So the basic meaning stays the same, but the emphasis can shift a little.

Yes. In Brazil, café da manhã is the standard and most widely used term for breakfast.

You may also hear people shorten it in casual speech, depending on context:

• o café

But café da manhã is the clearest and safest full expression.

A useful note:

• In European Portuguese, breakfast is commonly pequeno-almoço
• In Brazilian Portuguese, it is café da manhã

So for Brazilian Portuguese, your sentence uses the normal term.