Dakle, sve je spremno: pozivnice su poslane, čestitke napisane, a svjećice kupljene.

Dakle is a discourse word meaning so, therefore, well then, or in that case, depending on context. Here it introduces a conclusion or summary: So, everything is ready...

You can often leave it out if you want a more neutral sentence: Sve je spremno... = Everything is ready...

Because sve meaning everything is treated as neuter singular in Croatian. So it takes:

• je = singular is
• spremno = neuter singular form of spreman / spremna / spremno

So:

• Sve je spremno. = Everything is ready.

But if you name actual plural things, then you use plural agreement:

• Sve stvari su spremne. = All the things are ready.

It agrees with sve. In Croatian, adjectives and participles have to agree with the noun or pronoun they describe in gender and number.

Here:

• sve = neuter singular
• therefore spremno = neuter singular

Compare:

• On je spreman. = masculine singular
• Ona je spremna. = feminine singular
• Sve je spremno. = neuter singular

They are in the nominative plural, because they are the subjects of passive-style clauses:

• pozivnice su poslane
• čestitke (su) napisane
• svjećice (su) kupljene

That can be confusing because for these feminine plural nouns, the nominative plural and accusative plural look the same:

• pozivnice
• čestitke
• svjećice

So the form does not change here, but the grammatical role does.

These are passive participles (in Croatian grammar, glagolski pridjev trpni). They come from the verbs:

• poslati → poslane = sent
• napisati → napisane = written
• kupiti → kupljene = bought

With biti (je / su), they form a passive or resultative meaning:

• pozivnice su poslane = the invitations have been sent / are sent
• čestitke su napisane = the cards have been written
• svjećice su kupljene = the candles have been bought

In this sentence, the focus is on the finished state.

Because they agree with feminine plural nouns:

• pozivnice = feminine plural
• čestitke = feminine plural
• svjećice = feminine plural

So the participles also take the feminine plural form:

• poslane
• napisane
• kupljene

For comparison:

• masculine plural: poslani
• neuter plural: poslana
• feminine singular: poslana

It can be repeated, but Croatian often leaves it out when it is already understood from the previous clause.

The full version would be:

pozivnice su poslane, čestitke su napisane, a svjećice su kupljene

The sentence you have is a more natural, less repetitive version:

pozivnice su poslane, čestitke napisane, a svjećice kupljene

This kind of omission is very common in lists and coordinated clauses.

Here a is a coordinating conjunction. It can mean and, but, or while, depending on context. In this sentence, it works like a mild and, linking the last clause a bit more separately:

• ..., a svjećice kupljene.

You could also say i svjećice kupljene, but a sounds slightly more natural as a transition to the final item in a list of separate clauses. It gives a small sense of and as for the candles, those are bought too.

Yes, it is passive or result-focused in style. The sentence emphasizes that the tasks are completed, not who did them.

An active version would be:

Dakle, sve je spremno: poslali smo pozivnice, napisali čestitke i kupili svjećice.

That means:

• we sent the invitations
• we wrote the cards
• we bought the candles

So:

• passive/resultative = focus on the completed state
• active = focus on the people who did the actions

It can mean either, depending on context.

• Čestitke! often means Congratulations!
• But napisane čestitke clearly means written greeting cards / congratulatory cards / messages

So in this sentence, it does not mean someone is saying congratulations out loud. It means actual cards or written greetings.

Yes. This is completely correct:

Dakle, sve je spremno: pozivnice su poslane, čestitke su napisane, a svjećice su kupljene.

That version is a little more explicit and may feel easier for learners. The shorter version without repeated su is simply more compact and stylistically smoother.

Yes. Croatian word order is fairly flexible.

These are both possible:

• Pozivnice su poslane.
• Poslane su pozivnice.

The meaning stays basically the same, but the emphasis changes a little:

• Pozivnice su poslane focuses first on the invitations
• Poslane su pozivnice focuses first on the fact that they were sent

In your sentence, the noun-first order fits the checklist-like structure very well.

The colon introduces an explanation or list showing why everything is ready.

So this structure means:

• Everything is ready:
  • invitations sent,
  • cards written,
  • candles bought.

It is similar to English usage and works very naturally here.

A rough English approximation is SVYEH-chee-tseh, but with an important warning: the ć sound is softer than English ch.

A few useful points:

• j is pronounced like English y
• svje- is roughly svye-
• ć is softer than č
• c is pronounced ts

So:

• č as in čestitke = a harder ch sound
• ć as in svjećice = a softer sound, somewhere between ty and ch for many English speakers

You do not need perfect pronunciation right away; the main thing is to notice that č and ć are different letters in Croatian.