Eu preciso de dinheiro para pagar o aluguel.

Yes, you can often drop eu because the verb ending in preciso already shows it’s I.

• With subject: Eu preciso de dinheiro para pagar o aluguel.
• Without subject (very common): Preciso de dinheiro para pagar o aluguel.
  You’re more likely to keep eu for emphasis or contrast (e.g., Eu preciso, mas ele não precisa).

In Brazilian Portuguese, precisar is most commonly used with the preposition de when it means to need. The pattern is:

• precisar de + noun/pronoun → precisar de dinheiro, precisar de ajuda, precisar de você
  So de is not optional in normal usage with a noun like dinheiro.

Precisar can appear without de mainly in a more formal/less common structure where it’s followed by an infinitive, often meaning to need to:

• Common everyday: Preciso de dinheiro.
• Also possible: Preciso pagar o aluguel. (= I need to pay the rent.)
  But with a noun object (like dinheiro), Brazilian Portuguese typically uses precisar de.

Dinheiro is often used as an uncountable/general noun meaning money (in general), so it commonly appears with no article:

• Preciso de dinheiro. (= I need money.)
  If you say um dinheiro, it usually means a (certain) amount of money (often “a good amount” depending on context):
• Preciso de um dinheiro can sound like “I need some money / a sum of money.”
  o dinheiro usually refers to specific money already known in the conversation:
• Preciso do dinheiro (que você me deve). (= I need the money you owe me.)

Because dinheiro is used without an article in this sentence. Contractions happen when de + o/a/os/as occurs:

• de + o = do, de + a = da, etc.
  Examples:
• Preciso do dinheiro. (= I need the specific money.)
• Preciso da ajuda. (= I need the help.)

Para + infinitive is the standard way to express purpose: in order to pay.

• Formal/neutral: para pagar
• Very common in speech: pra pagar (a contraction of para)
  Both are correct; pra is more informal.

After para, Portuguese uses the infinitive to express purpose:

• para pagar = “to pay / in order to pay”
  It doesn’t conjugate because the subject is understood from context (here, the speaker).

Both are possible, with a small nuance:

• pagar o aluguel often sounds like pay the (specific) rent—the rent you have to pay (e.g., this month’s rent or your rent in general as a known obligation).
• pagar aluguel is also common and can sound slightly more general, like talking about the expense/category “rent.”
  In everyday Brazilian Portuguese, both are natural.

Aluguel refers to the rent (the payment), not the apartment itself.

• pagar o aluguel = to pay the rent
  The property is usually apartamento, casa, imóvel, etc.

Not in Brazil for this meaning. In Brazilian Portuguese:

• aluguel = rent (payment)
• renda = income/earnings (what you make), not rent
  So pagar a renda would sound wrong in Brazil.

Approximate Brazilian pronunciation (varies by region):

• Eu preciso → eh-OO preh-SEE-zoo (often the eu is reduced in fast speech)
• dinheiro → jee-NYEH-roo (the nh is like Spanish ñ; the ei is a diphthong)
• aluguel → ah-loo-GWELL (final -el often sounds like -éu/-éll depending on accent)