Tisíc korun je vysoká částka.

Because after tisíc (thousand), the counted noun normally appears in the genitive plural.

• koruna = crown / koruna
• nominative plural: koruny
• genitive plural: korun

So:

• tisíc korun = a thousand crowns
• compare also:
  • pět korun = five crowns
  • sto korun = a hundred crowns
  • milion lidí = a million people

This is a very common Czech pattern with numbers and quantity words.

Yes, but in normal everyday Czech, tisíc korun is much more natural.

• tisíc korun = the usual way to say one thousand crowns
• jeden tisíc korun sounds more explicit, contrastive, or formal

You might use jeden tisíc if you are emphasizing the number itself, for example in accounting, reading out figures, or contrasting it with another amount.

Because the whole phrase tisíc korun is treated as one amount, not as many separate coins or banknotes.

So Czech uses singular agreement:

• Tisíc korun je vysoká částka.
• literally: A thousand crowns is a high amount.

The idea is that one thousand crowns functions as a single quantity.

Czech often uses vysoký / vysoká / vysoké (high) with things like:

• prices
• sums of money
• salaries
• numbers
• costs

So vysoká částka is a very natural Czech expression for a high/large sum.

English usually says a high amount or more commonly a large sum, while Czech often prefers vysoká částka.

You may also hear:

• vysoká cena = a high price
• vysoký plat = a high salary
• vysoké náklady = high costs

Because it agrees with částka, which is:

• feminine
• singular
• nominative

In Czech, adjectives must agree with the noun they describe.

So:

• částka = feminine singular
• therefore vysoká částka

Compare:

• vysoký plat = high salary (plat is masculine)
• vysoké náklady = high costs (náklady are plural)

It is in the nominative.

In sentences with být (to be), the noun after the verb is often also in the nominative when it identifies or describes what something is.

So:

• Tisíc korun = subject
• je = is
• vysoká částka = predicate noun phrase, in the nominative

That is why you see částka, not something like částku.

You normally would not say Tisíc korun je vysoké by itself in this meaning.

The adjective vysoké would need a neuter noun to agree with, and there is no noun there. Czech usually wants the noun stated, such as:

• Tisíc korun je vysoká částka.
• Tisíc korun je vysoká suma.

But in everyday speech, people often avoid the noun completely by using another structure, for example:

• Tisíc korun je hodně. = A thousand crowns is a lot.
• To je hodně peněz. = That’s a lot of money.

Because Czech has no articles.

So where English says:

• a high amount
• the amount
• a thousand crowns

Czech simply uses the noun without an article:

• vysoká částka
• tisíc korun

Czech expresses definiteness and indefiniteness through context, word order, and sometimes other words, not through articles.

Yes, Czech word order is flexible, but the original order is the most neutral here:

• Tisíc korun je vysoká částka.

This presents tisíc korun as the topic and says something about it.

Other orders are possible, but they change emphasis. For example:

• Vysoká částka je tisíc korun.
  This sounds less neutral and would only fit a special context.

So for a learner, the given sentence is the best standard model.

No. korun is specifically the genitive plural form of koruna, so it appears wherever the grammar requires the genitive plural.

But yes, one of the most common places you will see it is after numbers and quantity expressions:

• pět korun
• sto korun
• tisíc korun

With other numbers, the form changes:

• jedna koruna
• dvě koruny
• tři koruny
• čtyři koruny
• pět korun

So learners often notice korun first in money expressions.

A rough English-friendly approximation is:

TI-seets KO-run yeh VI-so-kah CHA-stka

A few notes:

• ti in tisíc is soft
• c in Czech is like ts
• je sounds like yeh
• á is a long vowel
• stress in Czech is usually on the first syllable of each word:
  • TIsíc
  • KOrun
  • je
  • VIsoká
  • CHÁSTka

The spelling is quite regular, so once you learn Czech sound rules, pronunciation becomes much easier.

It is grammatical and natural, but it does sound a bit careful or explanatory.

In everyday conversation, a Czech speaker might more often say:

• Tisíc korun je hodně.
• To je dost peněz.
• To je vysoká částka.

But Tisíc korun je vysoká částka is still perfectly good Czech, especially in teaching materials or when speaking clearly and explicitly.