Я ранее работал здесь.

Because работал is the past tense form of работать (to work).

• я работаю = I work / I am working
• я работал = I worked / I used to work

In this sentence, the speaker is talking about an earlier time, so Russian uses the past tense.

Yes. In the past tense, Russian verbs agree with the subject in gender and number.

• я работал = a male speaker: I worked
• я работала = a female speaker: I worked
• мы работали = we worked

So this sentence would normally be said by a man. If a woman says it, it becomes Я ранее работала здесь.

Ранее means earlier, previously, or before in a fairly neutral or slightly formal way.

So Я ранее работал здесь means something like:

• I worked here previously
• I used to work here before
• I had worked here earlier

In everyday speech, learners will often hear раньше more often than ранее.

Both can mean earlier / before, but they are used a little differently.

• ранее = more formal, written, neutral, sometimes more official
• раньше = much more common in everyday speech

So:

• Я ранее работал здесь sounds correct, but slightly more formal or polished.
• Я раньше работал здесь sounds more natural in casual conversation.

A native speaker would probably say Я раньше работал здесь more often in normal speech.

Yes, Russian often drops subject pronouns when the meaning is clear from the verb.

So all of these are possible:

• Я ранее работал здесь.
• Ранее работал здесь.

Because работал already tells you it is singular past masculine, the subject can often be understood from context.

Still, Я is perfectly normal to include. It can make the sentence clearer or slightly more emphatic.

Yes, здесь and тут both mean here.

• здесь = neutral
• тут = also very common, often a bit more conversational

So these are both fine:

• Я ранее работал здесь.
• Я раньше работал тут.

The meaning is basically the same.
Just do not confuse здесь / тут (here, location) with сюда (to here, direction).

• Я работал здесь = I worked here
• Я пришёл сюда = I came here

Yes. Работал comes from работать, which is imperfective.

Russian uses the imperfective here because the sentence is describing:

• a past situation
• a fact about the past
• possibly repeated or ongoing activity
• not a single completed result

That fits English I worked here before or I used to work here.

A perfective verb would usually change the meaning. For example:

• поработал = worked for a while
• проработал = worked for a period of time / completed a span of employment

So Я ранее работал здесь is the natural broad statement.

It can suggest either one depending on context.

Most naturally, it means:

• I worked here before
• or I used to work here

Because работал is imperfective, it often gives a sense of past ongoing or habitual activity. But without more context, it does not strictly force one single English translation.

For example:

• if someone returns to an old workplace, it may mean I used to work here
• if someone is simply stating a past fact, it may mean I worked here before

Yes. Russian word order is flexible, and changing it usually changes emphasis, not the basic meaning.

Possible versions:

• Я ранее работал здесь.
• Ранее я работал здесь.
• Я работал здесь ранее.

These all mean roughly the same thing, but the focus shifts a little:

• Я ранее работал здесь = neutral
• Ранее я работал здесь = emphasizes previously
• Я работал здесь ранее = sounds a bit more formal or stylistically marked

In ordinary speech, Я раньше здесь работал or Я раньше работал здесь is very common.

Здесь is not a noun, so it does not take a case ending here. It is an adverb of place meaning here.

That is why the sentence does not need a preposition or case form after the verb:

• Я работал здесь = I worked here

Compare that with a noun phrase, which would need a case:

• Я работал в офисе = I worked in the office

Here в офисе uses the prepositional case, but здесь does not because it is an adverb.

Not if you want the same meaning.

• работал means worked
• находился means was located / was situated / was present

So:

• Я ранее работал здесь = I previously worked here
• Я ранее находился здесь = I was here earlier / I was previously located here

Those are different ideas.
If the meaning is about employment or doing work, работал is the right verb.

Yes, it is grammatically correct and natural, but it sounds a little more formal because of ранее.

In everyday conversation, many speakers would be more likely to say:

• Я раньше работал здесь.

So the original sentence is good Russian, especially in a more careful, formal, or written style.