Film tıpkı kitap gibi başladı.

Yes, gibi already means like / as.
The word tıpkı adds emphasis: exactly, just, precisely.

So:

• kitap gibi = like the book / like a book
• tıpkı kitap gibi = just like the book, exactly like the book

This tıpkı ... gibi pattern is very common in Turkish.

Gibi is a postposition. That means it comes after the word it relates to.

English uses a preposition:

• like the book

Turkish uses a postposition:

• kitap gibi
  literally: book like

So the order may feel reversed to an English speaker, but it is completely normal in Turkish.

Because kitap here is not a direct object. It is part of a comparison with gibi.

After gibi, a noun is normally used in its basic form:

• çocuk gibi = like a child
• rüya gibi = like a dream
• kitap gibi = like a book / like the book

So kitabı would not be the normal form here.

A useful thing to remember:

• -ı / -i / -u / -ü often marks a definite direct object
• but here kitap is not an object of the verb; it is the thing being compared to

Turkish does not use articles the same way English does.

There is no separate word exactly like English the.
And although bir can mean a / an, Turkish often leaves it out when it is not necessary.

So:

• film can mean the film or a film, depending on context
• kitap can mean the book or a book, depending on context

In this sentence, the intended meaning is understood from context, not from articles.

Başladı comes from the verb başlamak, meaning to start / to begin.

Breakdown:

• başla- = verb stem
• -dı = past tense suffix

So:

• başladı = started / began

This is 3rd person singular, and in Turkish that form does not need an extra ending here.

Examples:

• Film başladı. = The film started.
• Ders başladı. = The lesson started.

Because Turkish normally prefers verb-final word order.

A neutral Turkish sentence often looks like:

• Subject + other information + verb

So here:

• Film = subject
• tıpkı kitap gibi = comparison phrase
• başladı = verb

That gives:

• Film tıpkı kitap gibi başladı.

This is a very normal Turkish structure.

Yes, you can. It is grammatically possible.

• Film kitap gibi başladı. = The film started like the book.
• Film tıpkı kitap gibi başladı. = The film started just like the book.

The version with tıpkı is more emphatic and makes the similarity sound stronger or more exact.

Yes. Film is the subject.

It is in the basic form, with no special ending, because Turkish subjects are often just left in the plain form unless something else needs to be marked.

So the sentence structure is:

• Film = what is starting
• başladı = started

Everything in between gives extra information about how it started:
tıpkı kitap gibi = just like the book

It is understandable and grammatical, but depending on the exact meaning, Turkish speakers might sometimes choose a more specific version.

If the idea is the film began in the same way as it does in the book, a speaker might also say:

• Film tıpkı kitaptaki gibi başladı.

Here kitaptaki gibi means something like as in the book or the way it is in the book.

So:

• kitap gibi = more literally like the book
• kitaptaki gibi = like the version/information in the book

Your original sentence still works, but this is a nuance learners often notice later.

Because in Turkish, the noun comes before gibi.

So the normal order is:

• kitap gibi
• benim gibi
• çocuk gibi

not:

• gibi kitap

This is because gibi is a postposition, so it follows the word or phrase it belongs to.

In this sentence, it means to start / begin by itself.

• Film başladı. = The film started.

That is an intransitive use.

If you want to start something, Turkish often uses a different structure, for example:

• Filmi başlattı. = He/she started the film.

So:

• başladı = it started
• başlattı = he/she started it / caused it to start

That difference is very common in Turkish verbs.