He was the owner of a large territory; his wealth was so abundant that he was impressed (?).

"he was impressed" means that the king felt impressed. I think that you might mean to say he caused others to feel impressed. In which cause you need to specify who was impressed. You could say "his wealth was so abundant that he impressed everyone" for example.

One day he organized a contest that consisted of catching a beast feared by all, - that beast was a centaur.

The two clauses here are so disconnected that it reads better to use a larger stop than a comma. You could use a dash, semicolon, or just a full stop and split it into two sentences.

Peter, a humble tailor, knew that this story was only a myth, so he made up a plan.

As he had the ability to make disguises he created one so realistic that his relatives almost fainted when they saw it.

Then he arrived at the castle disguised as a centaur, along with his brother who was a guard at the castle, and his brother presented him to the king.

One part of the wealth was distributed to the poorest, and the other part was used to go and lived in another kingdom, where they created a huge clothing factory.

The kKing and Peter the tTailor

He was the owner of a large territory; his wealth was so abundant that even he was impressed.

The adverb “even” is used to emphasize a surprising statement.

Example: We all enjoyed the movie, even my grandmother liked it. (my grandmother doesn't like action movies)

It can also be used to emphasize a comparative*, like in this sentence you have written.

Example: The judges were so amazed by the performance that even Simon was surprised. (Simon is a very picky judge)

One day, he organized a contest that consisted of catching athe beast feared by all, that beast was ae centaur.

Peter, a humble tailor, knew that this story was only a myth, so he made up a plan.

When adding more information about the subject (the subject in this sentence is Peter), commas are placed between this block of information.

AsSince he had the ability to make disguises, he created one so real that his relatives almost fainted when they saw it.

Then he arrived atOn the day of the contest, he went to the castle disguised as a centaur, along with his brother, who was a guard at the castle. When they arrived, his brother presented him to the king.

ThenAfterwards, they collected the reward and escaped without a trace.

One part of the wealth was distributed to the poorest, and the other parrest of it was used to go andmove away to lived in another kingdom, where they created a huge clothing factory.