Imagine yourself beingas a young budding sailor inat the beginning of the nineteenth century.

Since your birth you've been dwelling in have lived in Marseille, the oldest town ofin France, Marcellies.

or "all your life"
in semi-formal writing you should probably omit contractions

Your future seems more than auspicious, and despite the fact that you are merely nineteen years of age, you were already granted a promotion to become the captain in just a few months.

merely + already = you don't need both

Furthermore, you are in mutual love with a young Corsican, and await to marry her in the nearest futurthe two of you are eager to marry as soon as possible.

"in mutual love" is not idiomatic English. It sounds odd.
"in the nearest future" is not idiomatic English either.

Everybody is utterly startlhocked, for your innocence is clear as day.

"startled" is for small surprises, like the unexpected sound of a phone ringing.
It does not pair well with "utterly" which is for big surprises

Why would anyone make such calumnious / slanderous accusations?

An extremely literary word "calumnious"

Nevertheless, omitting anywithout trials or explanations, you are being thrown into the most dreaded prison of France, Château d'If.

"omit" would be to forget or overlook something small imho

You, ntot even acquainted withally ignorant of your supposed crimes, are put into a solitary cell intended for despicable criminals.

Grammatically this is a stretch in English, placing so many words between "you" subject and "are" verb, but I think it's correct.
However "acquainted with" is too gentle for learning about crimes. I think the grammar police might prefer:
"You are put into a solitary cell intended for despicable criminals, without any idea of your supposed crimes."

Having spent thereAfter spending the most vigourous 14 years of your life andin prison, you acquired an abnormally enormous fortune, you and vow to avenge yourself.

This works if the fortune came all at once and precipitated the change.
If the fortune grew slowly over the years, you would need a different structure, such as
"Having spent the most vigorous 14 years of your life in prison, slowly acquiring an abnormally enormous fortune, you vow to avenge yourself."

It would not satiatesfy you to just dispatch the perpetrators, for what you have suffered exceeds that punishment immensely.

"satiate" is strongly associated with food and drink (at least for me). It sounds odd here.

Instead, you crave tohe annihilateion of everything they love, so that they couldwill feel at least the rea semblance of your anguish.

I can't explain, but "wish" would work in your sentence, but "crave" doesn't work the same way here

Do not get intimidated by its size, for if you like the first 100 pages, you will absolutely adore the rest.

"adore" is mostly for love of people, pets, passions--it feels a little over the top to say you adore a book.

The plot itself is quites intricate but engrossing, and the writing style is just fascinating.

I have read it in English, so several hundred of new literary words are a pretty{ } bonus.

"pretty" is too strongly associated with how something looks. Other words the internet suggests are "generous, hefty, welcome, pleasant" etc.

Beware of the spoilers!

Imagine yourself beingas a young budding sailor inat the beginning of the nineteenth century.

Since your birth, you've been dwellliving in the oldest town ofin France, Marcellies.

Your future seems more than auspicious, and(luck?) despite the fact that you are mebarely nineteen years of age, you werld. You have already been granted a promotion to become the captain in just a few months.