Learn Hardcore French: La rue est presque vide ce soir, c'est calme. - The street is almost empty tonight; it is calm.

French often uses c'est + adjective to comment on a situation as a whole. Here, c'est calme means the general atmosphere is quiet.
You could say Elle est calme to refer specifically to the street (since la rue is feminine), and it’s grammatical. The nuance:

C'est calme = a general, situational comment (very idiomatic).
Elle est calme = an attribute of the street itself; perfectly fine but feels a bit more like a property of that noun rather than a scene-wide comment.

Where does presque go and what does it mean?

Presque means almost/nearly. It goes right before the word it modifies:

Before an adjective: presque vide, presque prêt
Before an adverb: presque toujours
With verbs, it typically comes before the verb or (in compound tenses) before the past participle: il tombe presque, j’ai presque fini It can also combine with negatives: je ne sors presque jamais, il n’y a presque personne.

Is the comma before c'est calme correct in French?

Yes. In French, a comma can link two independent clauses more freely than in formal English. For a slightly more formal feel, use a semicolon or add a conjunction:

La rue est presque vide ce soir ; c’est calme.
La rue est presque vide ce soir, et c’est calme.

Can I say La rue est presque déserte instead of presque vide? What’s the difference?

Yes. Both are idiomatic.

(Presque) vide emphasizes emptiness in general (no cars, no people, no activity).
(Presque) déserte emphasizes a lack of people in particular and can sound a touch more literary.
So: La rue est presque déserte ce soir is a very natural alternative.

What’s the gender of rue, and how does that affect adjectives like vide or calme?

Rue is feminine: la rue. Adjectives agree with feminine nouns:

vide and calme already end with -e, so their feminine form looks the same: une rue vide, une rue calme.
Others change: désert → déserte (so: une rue déserte), animé → animée (une rue animée).

What’s the difference between ce soir, le soir, and dans la soirée?

ce soir = this evening/tonight (specific, deictic: the one happening today).
le soir = in the evening/evenings (habitual or general time of day).
dans la soirée = at some point later this evening/during the course of the evening (a time window).
Also useful: ce soir-là = that evening (in the past narrative).

Can ce soir go at the beginning of the sentence?

Yes. It’s common to front time expressions:

Ce soir, la rue est presque vide ; c’est calme. Putting ce soir first slightly emphasizes the time frame.

Could I rephrase it as Il n'y a presque personne dans la rue ce soir?

Absolutely. That focuses on the absence of people rather than describing the street itself. It’s very idiomatic.
Note the standard written negative: Il n’y a presque personne… (in informal speech, the ne is often dropped).

Why not il est calme after the comma?

Il est would normally refer back to a specific masculine noun (or a male person), not to the general situation. For situational comments, French uses c’est:

Good: …, c’est calme.
Possible if referring to the street with a pronoun: …, elle est calme.

Any pronunciation tips for this sentence?

La rue: [la ʁy]. The French u [y] is like “ee” with rounded lips; the r is uvular.
est: [ɛ] here.
presque: [pʁɛsk]; the final -e is very light or silent; -que = [k].
vide: [vid]; final -e is typically mute; the -d is pronounced.
ce soir: [sə swaʁ]; soir ends with a guttural r.
c’est: [sɛ].
calme: [kalm]; the final -e is typically mute.
No required liaisons in this line-up.

Does c'est need to agree in gender/number with anything?

No. Ce is invariable in c’est + adjective comments: C’est calme, C’était incroyable.
With plural nouns you switch to ce sont and then the noun/adjective agrees with the noun: Ce sont des rues calmes.
For the record, c’est is the elided form of ce est.

Can I use donc, et, or du coup to connect the clauses?

Yes, each with a nuance:

…, et c’est calme. neutral addition
…, donc c’est calme. logical consequence
…, du coup c’est calme. colloquial consequence (very common in speech)
Formal: … ; c’est calme.

Is there a way to specify what the street is empty of, like cars or people?

Yes:

La rue est vide de voitures. (devoid of cars)
La rue est presque déserte. (emphasizes few/no people)
More colloquial for people: Il n’y a presque pas de monde dans la rue. (hardly anyone on the street)

Is il fait calme acceptable?

Regionally, yes. In Belgian and Quebec French, il fait calme commonly means it’s quiet. In standard (Hexagonal) French, prefer c’est calme or phrases like il y a du calme; il fait calme is more about wind/weather there.