A vizinhança fica mais silenciosa à noite, e eu gosto de caminhar devagar pela calçada.

Because ficar often means to become or to get in Portuguese.

So A vizinhança fica mais silenciosa à noite means the neighborhood gets/becomes quieter at night, not that it is permanently quiet.

• é silenciosa = it is quiet
• fica silenciosa = it becomes / gets quiet

Here, fica suggests a change in condition as nighttime comes.

Because silenciosa agrees with a vizinhança, which is a feminine singular noun.

In Portuguese, adjectives usually agree in gender and number with the noun they describe:

• o bairro silencioso = the quiet neighborhood
• a vizinhança silenciosa = the quiet neighborhood / area

Since vizinhança is feminine singular, the adjective must also be feminine singular: silenciosa.

Vizinhança usually means neighborhood, the surrounding area, or sometimes the people living nearby, depending on context.

In this sentence, it means something like:

• the neighborhood
• the area around where I live

It is a little different from bairro, which is a more concrete administrative or geographic district/neighborhood.
So:

• bairro = neighborhood as a district
• vizinhança = neighborhood / nearby area / surroundings

Portuguese uses definite articles much more often than English.

So where English might simply say Neighborhoods get quieter at night or The neighborhood gets quieter at night, Portuguese naturally says:

• A vizinhança...

This is very normal. In Portuguese, a noun often sounds incomplete without its article unless it is being used in a very general or special way.

Mais silenciosa means quieter or literally more quiet.

Portuguese often forms the comparative with:

• mais + adjective

Examples:

• mais silenciosa = quieter
• mais bonita = prettier / more beautiful
• mais difícil = more difficult

So fica mais silenciosa = gets quieter.

Because à noite uses crase, which is the contraction of:

• the preposition a
• plus the feminine article a

So:

• a + a = à

The expression à noite means at night.

This happens in many common time expressions:

• à tarde = in the afternoon
• à noite = at night

But:

• de manhã = in the morning

So this is something you often just learn as a fixed expression.

Because the verb gostar requires the preposition de.

So in Portuguese, you say:

• gostar de + noun
• gostar de + infinitive

Examples:

• Eu gosto de música. = I like music.
• Eu gosto de caminhar. = I like walking / I like to walk.

Without de, the sentence would be ungrammatical.

Both can relate to walking, but they are not always identical.

• caminhar = to walk, often with a sense of walking as an activity
• andar = to walk, to go around, to move, and it has several other meanings too

In this sentence, caminhar sounds natural because it emphasizes the activity of walking, almost like strolling or taking a walk.

Compare:

• Gosto de caminhar. = I like walking.
• Gosto de andar pelo bairro. = I like walking around the neighborhood.

Both can work, but caminhar is a bit more specifically about the act of walking.

Devagar means slowly.

In eu gosto de caminhar devagar, it modifies caminhar, so it means I like to walk slowly.

Its position is normal after the infinitive:

• gosto de caminhar devagar

You may also hear adverbs in slightly different positions depending on emphasis, but this placement is the most natural here.

Yes, but devagar sounds much more natural in everyday speech here.

• caminhar devagar = very natural, conversational
• caminhar lentamente = correct, but a bit more formal or literary

In normal Brazilian Portuguese, devagar is the usual choice for this kind of sentence.

Pela is the contraction of:

• por + a = pela

And calçada means sidewalk.

So pela calçada means something like:

• along the sidewalk
• on the sidewalk
• through the sidewalk area, depending on context

It sounds natural because Portuguese often uses por/pela to express movement along or through a space.

Examples:

• andar pela rua = walk along the street
• caminhar pela praia = walk along the beach
• passar pela cidade = pass through the city

Yes, but the meaning shifts slightly.

• pela calçada emphasizes movement along the sidewalk
• na calçada emphasizes location on the sidewalk

So:

• caminhar pela calçada = walk along the sidewalk
• caminhar na calçada = walk on the sidewalk

Both are possible, but pela calçada fits especially well when you imagine the person moving along it.

Yes, it can be omitted.

Portuguese often drops subject pronouns when the verb already makes the subject clear:

• e eu gosto de caminhar...
• e gosto de caminhar...

Both are correct.

Including eu can add:

• emphasis
• contrast
• clarity

Here, eu is perfectly natural, especially if the speaker wants to sound slightly more personal: and I like to walk slowly...

Yes. Portuguese uses the present tense for habitual actions and general truths, just like English often does.

So:

• A vizinhança fica mais silenciosa à noite = the neighborhood gets quieter at night
• eu gosto de caminhar devagar pela calçada = I like to walk slowly along the sidewalk

This is not necessarily happening right now. It describes something generally true or habitual.

The original sentence already sounds natural. In speech, a Brazilian might also say things like:

• A vizinhança fica mais quieta à noite, e eu gosto de caminhar devagar pela calçada.
• À noite, a vizinhança fica mais silenciosa, e eu gosto de caminhar devagar pela calçada.

A small note:

• silenciosa is correct and natural
• quieta is also common in everyday speech and can feel a bit more colloquial in some contexts

So the given sentence is perfectly good Brazilian Portuguese.