Potrzebuję siedemdziesięciu złotych.

A word-for-word breakdown is:

• potrzebuję = I need
• siedemdziesięciu = seventy (in a declined form)
• złotych = złoty / zlotys in the form used here

So the whole sentence means I need seventy zlotys.

A more literal gloss would be something like I need of-seventy of-zlotys, because Polish uses cases here where English does not.

Potrzebować is the dictionary form, meaning to need.

In the sentence, you need the conjugated form:

• potrzebuję = I need

This is:

• 1st person singular
• present tense

So:

• potrzebuję = I need
• potrzebujesz = you need
• potrzebuje = he/she/it needs

Polish verbs usually change their endings depending on the person, so you cannot normally leave them in the dictionary form in a sentence like this.

Because potrzebować usually takes the genitive case in Polish.

That means the thing needed is put into genitive, not the basic dictionary form.

So compare:

• dictionary/basic number: siedemdziesiąt
• after potrzebuję: siedemdziesięciu

And:

• dictionary/basic noun: złoty
• here: złotych

This is one of the most important things to remember with potrzebować:

• potrzebuję czasu = I need time
• potrzebuję pieniędzy = I need money
• potrzebuję siedemdziesięciu złotych = I need seventy zlotys

Because siedemdziesiąt is the basic form of seventy, but after potrzebuję you need the genitive form.

For siedemdziesiąt, the genitive form is siedemdziesięciu.

So:

• siedemdziesiąt = basic form
• siedemdziesięciu = genitive form

This happens with many higher numbers in Polish when the grammar requires a case change.

Because with numbers like 70, Polish uses the noun in the genitive plural.

The forms are:

• 1 złoty
• 2, 3, 4 złote
• 5+ złotych

Since 70 belongs to the 5+ group, you get:

• siedemdziesiąt złotych

And because the whole phrase is also governed by potrzebuję, the numeral changes too:

• potrzebuję siedemdziesięciu złotych

So złotych is exactly what you should expect with 70.

In standard Polish, no — that would be incorrect.

After potrzebować, you should use the genitive:

• Potrzebuję siedemdziesięciu złotych.

Using siedemdziesiąt here keeps the number in its basic form, but the verb requires a different case.

So the correct version is:

• potrzebuję siedemdziesięciu złotych

No. Polish usually leaves out subject pronouns when they are clear from the verb ending.

• Potrzebuję already means I need
• So ja is not necessary

You can say:

• Potrzebuję siedemdziesięciu złotych.

If you say:

• Ja potrzebuję siedemdziesięciu złotych.

that is still correct, but it adds emphasis, something like:

• I need seventy zlotys
• or Me, I need seventy zlotys

No, Polish word order is fairly flexible.

The most neutral order here is:

• Potrzebuję siedemdziesięciu złotych.

But other orders are possible for emphasis, for example:

• Siedemdziesięciu złotych potrzebuję.

That version puts stronger focus on the amount of money.

For learners, the safest and most natural choice is the original order:

• Potrzebuję siedemdziesięciu złotych.

A rough English-friendly guide is:

• Potrzebuję ≈ poh-tsheh-BOO-yeh
• siedemdziesięciu ≈ shyeh-dem-jye-SHYEHN-chyoo
• złotych ≈ ZWO-tikh

A few useful pronunciation notes:

• rz is usually pronounced like the s in measure
• si before a vowel often sounds like sh with a softer quality
• ę at the end of potrzebuję is often pronounced close to -e / -ye in normal speech
• ł sounds like English w
• ch sounds like the ch in Scottish loch or German Bach

If you want a simpler approximation of the whole sentence:

• poh-tsheh-BOO-yeh shyeh-dem-jye-SHYEHN-chyoo ZWO-tikh

Potrzebować is imperfective.

In this sentence, that mainly matters because you are using a normal present-tense form:

• potrzebuję = I need

For everyday use, the key thing to remember is not aspect, but the fact that potrzebować governs the genitive.

So for this sentence, the most important grammar point is:

• potrzebować + genitive

not aspect.

Yes, it is a perfectly natural sentence.

It could be used in situations like:

• needing money to buy something
• telling someone how much money you need
• explaining a shortage

For example:

• Potrzebuję siedemdziesięciu złotych na bilet. = I need seventy zlotys for a ticket.

In casual speech, a speaker might also say:

• Potrzebuję jeszcze siedemdziesięciu złotych. = I still need seventy zlotys.

But the original sentence is completely normal and correct on its own.