Sutra ću se probuditi rano, jer putujem vozom.

Both patterns exist in Serbian.

In this sentence, ću is the short form of hteti used to make the future, and it appears as a clitic, which usually goes in the second position of the clause:

• Sutra ću se probuditi rano.

You can also say:

• Probudiću se sutra rano.

So these are both natural:

• Sutra ću se probuditi rano.
• Probudiću se sutra rano.

Very roughly:

• if the infinitive stays after the clitic, you get ću + infinitive
• if the verb comes first, the future ending attaches to it: probudiću

Both mean the same thing here.

Ću is the 1st person singular short future form of the verb hteti (to want), but in modern Serbian it is also used as an auxiliary to form the future tense.

The full set is:

• ja ću = I will
• ti ćeš = you will
• on/ona/ono će = he/she/it will
• mi ćemo = we will
• vi ćete = you will
• oni/one/ona će = they will

So in Sutra ću se probuditi rano, ću means I will.

Probuditi se means to wake up, while probuditi without se usually means to wake someone/something up.

Compare:

• Probudila sam se. = I woke up.
• Probudila sam dete. = I woke up the child.

So se is needed here because the speaker is the one waking up.

This is an aspect difference, which is very important in Serbian.

• buditi se = imperfective
• probuditi se = perfective

In simple terms:

• buditi se focuses on the process, repetition, or habit
• probuditi se focuses on the completed event

Here, the speaker means I will wake up as a single completed action tomorrow, so probuditi se is the natural choice:

• Sutra ću se probuditi rano.

If you said Sutra ću se buditi rano, it would sound more like Tomorrow I’ll be waking up early / I’ll have to wake up early repeatedly / as a process, which is less natural in this context.

Serbian often uses the present tense for a future action when the future event is planned, arranged, scheduled, or certain from context.

So:

• jer putujem vozom = because I’m traveling by train

Even though it is about tomorrow, the present tense sounds natural because the trip is understood as a real planned event.

English does something similar:

• I’m leaving tomorrow.
• My train leaves at 7.

Serbian can do the same:

• Sutra putujem. = I’m traveling tomorrow.

Because vozom is the instrumental singular of voz (train), and Serbian uses the instrumental case after a verb to express means of transport.

So:

• putujem vozom = I travel by train

Other examples:

• Idem autobusom. = I’m going by bus.
• Putujemo kolima. = We’re traveling by car.
• Došao je avionom. = He came by plane.

So vozom answers the question by what means?

Serbian word order is fairly flexible, but it is not completely free. One important rule is that short unstressed words such as ću and often se behave like clitics, and they tend to appear near the beginning of the clause, usually in second position.

That is why this order is natural:

• Sutra ću se probuditi rano.

Here:

• Sutra comes first for emphasis/time setting
• ću se comes right after it

You may also hear:

• Ja ću se sutra probuditi rano.
• Probudiću se sutra rano.

All are possible, but the original sentence is very standard and natural.

Yes, absolutely.

Both are possible:

• jer putujem vozom
• jer ću putovati vozom

The difference is mostly one of style and nuance:

• jer putujem vozom sounds like a planned or arranged future event, very natural in everyday speech
• jer ću putovati vozom is a more explicit future form

Also notice the aspect:

• putujem is from putovati (imperfective)
• ću putovati is also future with the imperfective verb

In this sentence, the present tense version sounds especially natural.

Jer means because.

So:

• Sutra ću se probuditi rano, jer putujem vozom.

You can also say:

• Sutra ću se probuditi rano zato što putujem vozom.

Both mean because, but:

• jer is shorter and very common
• zato što is also common and sometimes sounds slightly more explicit

Both are correct here.

Because Serbian usually does not need a subject pronoun when the verb form already shows who the subject is.

In:

• ću
• putujem

it is already clear that the subject is I.

So ja is usually omitted unless you want to add emphasis or contrast:

• Ja ću se probuditi rano, a ti nećeš. = I will wake up early, but you won’t.

Without emphasis, leaving out ja is more natural.

No. Rano here is an adverb, meaning early, so it does not change for gender, number, or case.

Compare:

• rano = early (adverb)
• rani / rana / rano = early (adjective forms)

In the sentence:

• probuditi se rano = to wake up early

Since it describes how the action happens, it is an adverb.

Yes:

• Ja ću se probuditi rano, jer putujem vozom.

This is grammatically correct, but it changes the emphasis slightly.

Compare:

• Sutra ću se probuditi rano... = emphasis on tomorrow
• Ja ću se probuditi rano... = emphasis on I

In many contexts, Serbian prefers not to say ja unless it is needed, so the original sentence sounds more natural if there is no special contrast.