Kad sastanak završi, ići ćemo na kavu.

Here kad means when.

Yes, kad and kada mean the same thing. The main difference is style:

• kad = shorter, very common in everyday speech
• kada = a bit more formal or fuller-sounding

So:

• Kad sastanak završi...
• Kada sastanak završi...

Both are correct.

Because Croatian often uses the present tense in a time clause after words like kad to talk about a future event.

So Kad sastanak završi literally looks like When the meeting finishes, even though it refers to the future.

This is actually similar to English:

• When the meeting finishes, we’ll go for coffee.

English also uses present tense after when, not will finish.

So Croatian is doing something very natural here.

This is about aspect, which is very important in Croatian.

• završiti = to finish / to complete once, as a completed event
  
  • perfective
• završavati = to be finishing / to finish repeatedly or habitually
  
  • imperfective

In this sentence, we mean the moment the meeting is finished, as one completed action. So Croatian uses the perfective verb:

• Kad sastanak završi...

If you used završava, it would sound more like an ongoing or repeated process, which does not fit as well here.

završi is the 3rd person singular present form of završiti.

Why 3rd person singular? Because the subject is sastanak = meeting, which is singular:

• sastanak završi = the meeting finishes

So the verb agrees with sastanak.

ići ćemo is the Croatian future tense.

It is made from:

• the infinitive ići = to go
• the auxiliary ćemo = we will

So:

• ići ćemo = we will go

This is the 1st person plural, meaning we.

Because Croatian often omits subject pronouns when they are already clear from the verb form.

In ćemo, the ending already tells you the subject is we.

So Croatian does not need mi here.

• ići ćemo na kavu = we will go for coffee
• mi ćemo ići na kavu = also possible, but mi adds emphasis

You would use mi if you want contrast or emphasis, like we will go, not they.

Yes, absolutely.

These are both correct:

• Ići ćemo na kavu.
• Mi ćemo ići na kavu.

The version without mi is more neutral and natural in many situations.

The version with mi sounds more emphatic, for example:

• Mi ćemo ići na kavu, a oni će ostati ovdje.
  We will go for coffee, and they will stay here.

Because Croatian uses na + accusative for many activities, outings, and destinations of this type.

So:

• ići na kavu = to go for coffee
• ići na ručak = to go for lunch
• ići na posao = to go to work

Here, kava changes to kavu because na with movement usually takes the accusative case.

• nominative: kava
• accusative: kavu

So:

• na kavu

Grammatically, it is singular, but idiomatically it usually means to go have coffee / meet for coffee.

It does not necessarily mean exactly one cup of coffee per person.

It often refers to the whole social activity, much like English go for coffee.

So even if people drink something else, Croatians may still say:

• Idemo na kavu.

Because Croatian has no articles.

There is no direct equivalent of English a or the used before nouns in normal Croatian grammar.

So sastanak can mean:

• a meeting
• the meeting

Context tells you which one is meant. In this sentence, it will usually be understood as the meeting because both speakers know which meeting they are talking about.

Because Kad sastanak završi is a dependent time clause placed before the main clause.

Croatian normally separates that kind of introductory clause with a comma:

• Kad sastanak završi, ići ćemo na kavu.

This is similar to English punctuation:

• When the meeting finishes, we’ll go for coffee.

Yes. You can also say:

• Ići ćemo na kavu kad sastanak završi.

This means the same thing.

The difference is mainly in emphasis and flow:

• Kad sastanak završi, ići ćemo na kavu.
  starts with the time condition
• Ići ćemo na kavu kad sastanak završi.
  starts with the main action

Both are natural.