U novom stanu imamo više prostora nego prije.

Because u can take two different cases:

• locative for being in a place
• accusative for movement into a place

Here the sentence describes a location: In the new apartment, we have..., so Croatian uses the locative:

• u novom stanu = in the new apartment

If it meant movement, it would be:

• Idemo u novi stan. = We are going into the new apartment / moving to the new apartment.

Because the adjective has to agree with the noun in gender, number, and case.

• stan is masculine singular
• after u with location, it is in the locative singular
• so the adjective must also be masculine singular locative

That gives:

• novom stanu = in the new apartment

So novom is simply the correct locative singular form of novi.

Croatian often leaves out subject pronouns because the verb ending already tells you who the subject is.

• imamo = we have

So there is no need to say mi unless you want emphasis or contrast:

• Mi imamo više prostora nego prije. = We have more space than before.

That sounds more emphatic, like we (not someone else).

Imamo is the 1st person plural present tense of imati (to have).

So:

• imam = I have
• imaš = you have
• ima = he/she/it has
• imamo = we have
• imate = you all / you formal have
• imaju = they have

In this sentence, imamo tells you the subject is we.

Više means more.

In this sentence it works as a quantity word:

• više prostora = more space

It does not change form here. You will often see više used in comparisons:

• više vremena = more time
• više novca = more money
• više soba = more rooms

Because after words like više (more), Croatian usually puts the noun in the genitive.

So:

• prostor = space
• više prostora = more space

This is very common after expressions of quantity. Compare:

• puno vremena = a lot of time
• malo novca = little money
• dosta ljudi = enough / quite a lot of people

With space, English does not show a case change, but Croatian does.

Because prostor here is being used as an uncountable / mass noun, like space in English.

So Croatian treats it like a substance or amount:

• više prostora = more space

That is why you get the genitive singular form prostora, not a plural meaning spaces.

If you were talking about countable things, you would often get a plural noun instead:

• više soba = more rooms
• više stolica = more chairs

In comparisons, Croatian often uses nego to mean than.

Here:

• više prostora nego prije = more space than before

This is the standard way to compare one amount with another state or time.

A useful pattern is:

• više ... nego ... = more ... than ...
• manje ... nego ... = less ... than ...

Examples:

• Više radi nego prije. = He/She works more than before.
• Stan je veći nego prije. = The apartment is bigger than before.

Here prije means before or earlier.

In this sentence it is being used adverbially, so it stands on its own:

• nego prije = than before

It does not take a noun here.

But prije can also be a preposition, in which case it takes the genitive:

• prije ručka = before lunch
• prije posla = before work

So in your sentence, prije is just an adverb meaning before / earlier.

Yes:

• U novom stanu mi imamo više prostora nego prije.

That is grammatically correct, but mi is usually unnecessary unless you want emphasis, contrast, or clarity.

Without mi, the sentence sounds more natural in neutral everyday Croatian.

Yes, Croatian word order is fairly flexible, though not completely free.

The original sentence:

• U novom stanu imamo više prostora nego prije.

is natural and puts the setting in the new apartment first.

You could also say:

• Imamo više prostora u novom stanu nego prije.

That is also understandable, but the emphasis shifts slightly.

Croatian often moves parts of the sentence around for focus, topic, or style, while the case endings keep the meaning clear.

Because Croatian has no articles.

English distinguishes:

• a new apartment
• the new apartment

Croatian does not have separate words like a or the. So:

• u novom stanu

can mean either:

• in a new apartment
• in the new apartment

The exact meaning depends on context.

It may feel incomplete from an English learner’s point of view, but in Croatian this is perfectly normal.

• nego prije means than before
• the earlier situation is understood from context

In this sentence, the idea is:

• we have more space now than we had before

Croatian often leaves that implied if it is obvious.

Sometimes yes, but prije is the most natural choice here.

• nego prije = than before

Ranije means earlier, and it can work in some contexts, but in this kind of everyday comparison prije is more idiomatic.

So for this sentence, a learner should strongly prefer:

• više prostora nego prije

over:

• više prostora nego ranije

Even if the second one may be understandable.