Eu preciso me cadastrar hoje.

Yes. In Portuguese, subject pronouns are often omitted when the verb ending already makes the subject clear.

So:

• Eu preciso me cadastrar hoje.
• Preciso me cadastrar hoje.

Both are natural and mean the same thing.

You might keep eu for:

• emphasis
• contrast
• extra clarity

For example, Eu preciso me cadastrar hoje, mas ele não emphasizes I.

Preciso is the I form of the verb precisar, which usually means to need.

So:

• eu preciso = I need

In this sentence, it is followed by another verb:

• preciso me cadastrar = I need to register / sign up

A very common pattern is:

• precisar + infinitive verb
  = to need to do something

Examples:

• Preciso estudar. = I need to study.
• Preciso sair. = I need to leave.

Because cadastrar-se is commonly used as a reflexive-style verb in Portuguese when the subject is registering themself.

So:

• me cadastrar = register myself / sign myself up

Here, me matches eu:

• eu ... me cadastrar

Other forms would be:

• você precisa se cadastrar
• ele precisa se cadastrar
• nós precisamos nos cadastrar

In everyday Brazilian Portuguese, cadastrar-se often means to sign up, to register, or to create a registration for yourself.

Cadastrar usually means to register, to enter into a system, to sign up, or to put on file.

In Brazil, it is very common in situations like:

• websites
• apps
• stores
• government systems
• job platforms
• customer databases

So me cadastrar often means:

• sign myself up
• create an account
• register myself in the system

It is similar to registrar-se in some contexts, but cadastrar-se is especially common in Brazilian everyday administrative and online language.

Both are grammatically possible, but in Brazilian Portuguese, me cadastrar is much more natural in normal speech and informal writing.

So:

• Preciso me cadastrar hoje. = natural, common in Brazil
• Preciso cadastrar-me hoje. = grammatical, but more formal or less common in everyday Brazilian usage

Brazilian Portuguese strongly prefers placing object/reflexive pronouns before the infinitive in many everyday situations.

Usually no, not if you mean I need to register myself.

Without me, the sentence sounds incomplete or changes meaning. Cadastrar without a reflexive pronoun often means registering someone or something else.

Compare:

• Preciso me cadastrar hoje. = I need to register myself today.
• Preciso cadastrar o cliente hoje. = I need to register the client today.
• Preciso cadastrar meus dados hoje. = I need to register my information today.

So if the subject is registering themself, me is normally needed.

Because Portuguese uses two different patterns with precisar:

• precisar de + noun
• precisar + infinitive verb

Here you have an infinitive verb, cadastrar, so de is not used:

• Preciso me cadastrar. = I need to register.

But with a noun:

• Preciso de ajuda. = I need help.
• Preciso de um documento. = I need a document.

So preciso de me cadastrar is not the normal pattern here.

Yes. Hoje means today, and its position is fairly flexible.

All of these are possible:

• Eu preciso me cadastrar hoje.
• Hoje eu preciso me cadastrar.
• Eu hoje preciso me cadastrar.

The most neutral and natural version is often:

• Eu preciso me cadastrar hoje.

If you put hoje first, it gives a little more focus to today:

• Hoje eu preciso me cadastrar. = Today, I need to register.

Not always. It can be used in two main ways:

1. Reflexive / intransitive-style

   • Eu vou me cadastrar no site.
   • I’m going to register on the website.

2. Transitive

   • Vou cadastrar você no sistema.
   • I’m going to register you in the system.

So the verb can mean either:

• register oneself or
• register someone/something

That is why the pronoun matters so much.

A simple approximate pronunciation for an English speaker is:

• eh-ooh preh-SEE-zoo mee kah-dahs-TRAR OH-zhee

A few helpful notes:

• preciso has stress on ci: preh-SEE-zo
• cadastrar has stress on the last syllable: cadas-TRAR
• hoje in Brazil sounds roughly like OH-zhee or OH-jee, depending on accent
• the r at the end of cadastrar may sound softer in many Brazilian accents

You do not need to pronounce it exactly like English spelling suggests. The key stresses are:

• preCIso
• cadasTRAR
• HOje

Yes. Some common alternatives are:

• Tenho que me cadastrar hoje. = I have to register today.
• Devo me cadastrar hoje. = I should / am supposed to register today.

The nuance changes a little:

• preciso = need to
• tenho que = have to
• devo = should / ought to / am expected to

In many everyday situations, preciso me cadastrar hoje and tenho que me cadastrar hoje are both very common.