Eu gosto de torrada com geleia no café da manhã.

Because gostar normally takes the preposition de in Portuguese.

• gostar de + noun
• gostar de + verb

So:

• Eu gosto de torrada.
• Eu gosto de café.
• Eu gosto de viajar.

This is one of those verb patterns you simply have to learn with the verb.

Yes. Very often, you can simply say:

• Gosto de torrada com geleia no café da manhã.

Portuguese often drops subject pronouns when the verb form already makes the subject clear.
Gosto clearly means I like, so eu is optional here.

You might keep eu for emphasis, contrast, or clarity:

• Eu gosto de torrada, mas meu irmão não gosta.

Both singular and plural are possible, depending on what you mean.

• torrada can mean toast in a general sense
• torradas can suggest multiple pieces or servings

So these can both sound natural:

• Eu gosto de torrada com geleia no café da manhã.
• Eu gosto de torradas com geleia no café da manhã.

The singular here works well as a general food item, not necessarily one single piece.

Com geleia means with jam/jelly and describes how the toast is eaten.

So the structure is:

• gosto de = I like
• torrada com geleia = toast with jam/jelly
• no café da manhã = at/for breakfast

In other words, com geleia modifies torrada.

No is the contraction of:

• em + o = no

So:

• no café da manhã = literally in the breakfast, but naturally at breakfast or for breakfast

Portuguese very often contracts prepositions with articles:

• de + o = do
• de + a = da
• em + o = no
• em + a = na

That is also why you see da manhã:

• de + a manhã = da manhã

Literally, café da manhã means coffee of the morning, but this whole expression means breakfast.

It is a fixed expression in Portuguese:

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

So you should learn café da manhã as one chunk.

Portuguese often uses articles where English does not.

Here, no includes the masculine singular article o, because café is masculine:

• o café da manhã
• no café da manhã

This is very normal in Portuguese. English and Portuguese do not always match in article usage.

Yes, but the meaning shifts a little.

• no café da manhã = at breakfast / for breakfast, focusing on the time or meal context
• para o café da manhã = for breakfast, often emphasizing purpose

Examples:

• Eu gosto de torrada com geleia no café da manhã.
  I like toast with jam at breakfast.

• Eu faço torrada com geleia para o café da manhã.
  I make toast with jam for breakfast.

In your original sentence, no café da manhã sounds very natural.

Yes. In modern Brazilian Portuguese, geleia is the standard spelling.

You may sometimes see geléia in older texts, but that spelling is outdated after spelling reforms.

So for contemporary Brazilian Portuguese, use:

• geleia

Yes, a little, though the original order is the most straightforward.

Natural version:

• Eu gosto de torrada com geleia no café da manhã.

You could also hear:

• No café da manhã, eu gosto de torrada com geleia.

That version puts emphasis on at breakfast.

In general, Portuguese allows some flexibility in word order, but the original sentence is a very standard, neutral way to say it.

Just put não before the verb:

• Eu não gosto de torrada com geleia no café da manhã.

This is the normal way to negate a sentence in Portuguese:

• eu gosto = I like
• eu não gosto = I don’t like

In spoken Brazilian Portuguese, you can usually keep the same word order and use rising intonation:

• Você gosta de torrada com geleia no café da manhã?

Or with eu:

• Eu gosto de torrada com geleia no café da manhã?

That second one would usually sound like you are checking or repeating, not making a normal question about yourself.

A more typical question would be:

• Você gosta de torrada com geleia no café da manhã?

Portuguese does not always require changing word order to form a question.