Learn Hardcore Croatian: Da imam više novca, ljeto bih provela na moru. - If I had more money, I would spend the summer at the sea.

Literally it’s something like That I have more money, but functionally it works like if in this kind of conditional sentence.
In more formal or textbook Croatian you’ll also see:

Kad bih imala više novca…
Ako bih imala više novca…

All three can express a hypothetical situation, but da + present is very common in everyday speech.

Why is it imam (present tense) if the English uses had (past tense)?

Croatian doesn’t copy English tenses in conditionals. Here we have the pattern:

da + present tense (da imam)
conditional (bih provela)

This combination expresses an unreal / hypothetical situation in the present or future, like English If I had… I would spend…

So:

imam is grammatically present tense, but in this construction da + present has an irrealis (unreal) meaning.
English chooses a past tense (had) to signal unreal condition. Croatian signals it through this da + present + conditional structure instead.

What exactly is bih? Is it a separate verb from provela?

Bih is the conditional form of the auxiliary verb biti (to be).

The Croatian conditional is formed with:

a conditional auxiliary (bih, bi, bismo, biste, bi)
a past participle (provela)

So bih provela = would spend.

You can think of it like this:

bih = would
provela = spent

Together they make the conditional: I would spend.

Why is it provela and not proveo?

Provela/proveo is a past participle, and in Croatian past participles agree in gender (and number) with the subject.

proveo – masculine singular
provela – feminine singular

The sentence assumes a female speaker (ja = I, female), so you say:

(Ja) bih provela… if the speaker is female
(Ja) bih proveo… if the speaker is male

Where is the subject in this sentence? I don't see a word for I.

The subject is implied: ja (I).

In Croatian, subject pronouns are often dropped because the verb form (or participle) already shows the person and gender.

bih indicates 1st person singular (I would)
provela indicates feminine singular (so I [female] would have spent)

So the full version would be: Ja bih provela ljeto na moru, but ja is usually omitted unless you want to emphasise I.

Why is ljeto in the accusative with no preposition? Why not something like u ljetu?

Ljeto is used here as an adverbial accusative of time. Croatian often uses the bare accusative of a time word to mean during [that time].

Examples:

Ove godine putujem u Hrvatsku. – This year I am travelling to Croatia.
Svaku zimu idem na planinu. – Every winter I go to the mountains.
Ljeto bih provela na moru. – I would spend (the) summer at the seaside.

U ljetu would sound unusual in this context. The natural way to say (the) summer as the time when something happens is just ljeto in the accusative without a preposition.

Why is it više novca instead of više novac?

Više (more) is a quantity word, and in Croatian such words usually require the genitive case after them.

novac – nominative (dictionary form)
novca – genitive singular

After više, you put the noun in the genitive:

više novca – more money
više vremena – more time
više prijatelja – more friends

So više novac would be ungrammatical; it has to be više novca.

What’s the difference between više novca and puno novca?

Both use novca (genitive), but the meanings differ:

više novca – more money (comparative: more than some previous amount)
puno novca – a lot of money / much money (large quantity, not necessarily a comparison)

Grammar:

both više and puno are followed by genitive:
- više novca
- puno novca

Why is it na moru and not just more or something like u moru?

Several things are happening here:

na
- locative:
- na moru: at the sea / at the seaside (location)
- more is nominative; locative is moru.
Idiomatic meaning:
- na moru means being/staying at the seaside (on the coast, on vacation).
- u moru would mean in the sea (literally in the water, not on the beach or at a resort).

So ljeto bih provela na moru = I would spend the summer at the seaside, not literally in the sea.

Why is the form moru used instead of more?

More (sea) is a neuter noun that changes with case:

Nominative: more (the sea – subject)
Genitive: mora
Dative/Locative: moru

After the preposition na with a static meaning (location, not movement), you generally use the locative case:

na moru – at the sea(seaside)
na stolu – on the table
na poslu – at work

So na moru is na + locative (moru), not nominative (more).

Why does bih appear in the second position in the clause ljeto bih provela, and not at the beginning?

Croatian has a rule that short unstressed words (clitics) like bih, bi, sam, si, mi, ti normally go in “second position” in a clause.

They usually come after the first stressed word or phrase in the sentence.

In your example:

First element: ljeto
Second position: bih
Then the main verb: provela

So:

Ljeto bih provela na moru. – natural
Bih ljeto provela na moru. – sounds wrong; clitics don’t normally go first.

Can I change the word order and say Provela bih ljeto na moru? Does it mean the same thing?

Yes, you can say Provela bih ljeto na moru, and it means the same thing.

Both are correct:

Ljeto bih provela na moru.
Provela bih ljeto na moru.

The difference is nuance/emphasis:

Ljeto bih provela na moru. slightly highlights when you’d spend time at the seaside – the summer.
Provela bih ljeto na moru. is a bit more neutral or focuses a bit more on the action provela (I would spend).

In both versions, bih stays in second position: after the first stressed word (ljeto or provela).

Could I also say Kad bih imala više novca, ljeto bih provela na moru? Is there any difference from Da imam više novca…?

Yes, you can say:

Kad bih imala više novca, ljeto bih provela na moru.

This is also a correct unreal conditional: If I had more money, I would spend the summer at the seaside.

Differences:

Da imam više novca… – very common in everyday speech; compact; uses da + present to show unreality.
Kad bih imala više novca… – more explicit standard conditional form; you see bih + past participle in the if-clause as well.

In practice, both sound natural. Da imam… may feel a bit more colloquial/idiomatic; Kad bih imala… is more transparently conditional.

Does the conditional auxiliary bih need to appear in both clauses, or only in the second one?

In this particular structure da + present + conditional, the conditional auxiliary bih appears only in the result clause:

Da imam više novca, ljeto bih provela na moru.

You do not say:

Da bih imala više novca, ljeto bih provela na moru. ← different pattern, feels more formal/bookish and not the same structure.

If you use kad/ako with a standard unreal conditional, then bih often appears in both clauses:

Kad bih imala više novca, ljeto bih provela na moru.
Ako bih imala više novca, ljeto bih provela na moru.

So:

da + present → no bih in the da-clause
kad/ako + bih + past participle → bih can be in both clauses.