En cuanto terminó la grabación, empezamos la edición.

Here en cuanto means as soon as.

It emphasizes that the second action happened immediately after the first one:

• En cuanto terminó la grabación, empezamos la edición. = As soon as the recording finished, we started the editing.

You could also say cuando terminó la grabación, but en cuanto sounds more specifically immediate.
So:

• cuando = when
• en cuanto = as soon as / once

Terminó is the preterite tense, which is used for a completed action at a specific point in the past.

In this sentence, the recording finished, and then another action followed. That makes the preterite the natural choice:

• terminó = finished
• terminaba = was finishing / used to finish

If you said terminaba, it would sound more like background action or an ongoing process, which does not fit as well with the idea of one completed event triggering another.

Yes, empezamos can be either:

• present: we start
• preterite: we started

This is one of those forms that look identical in Spanish.

In this sentence, the context clearly shows it is preterite because it is describing a finished sequence in the past:

• first, terminó la grabación
• then, empezamos la edición

So here empezamos means we started, not we start.

Spanish often uses the definite article (el, la, los, las) in places where English might leave it out.

Here, la grabación and la edición refer to specific stages or processes:

• la grabación = the recording
• la edición = the editing / editing stage

In English, you might sometimes say recording or editing without the, but Spanish commonly includes the article in this kind of context.

Yes. Acabó and terminó are both natural here.

Both mean something like finished / ended:

• En cuanto terminó la grabación...
• En cuanto acabó la grabación...

In many contexts they are interchangeable.
Terminar can sound slightly more neutral or formal, while acabar is also very common in everyday Spanish.

Because Spanish usually does not need subject pronouns when the verb ending already tells you who the subject is.

• empezamos already shows we
• terminó already shows he/she/it or a singular noun subject

So:

• empezamos la edición = we started the editing

Adding nosotros is possible, but it is usually only done for emphasis or contrast.

Because here en cuanto is a fixed conjunction meaning as soon as.

Spanish uses cuanto without an accent in this kind of connector expression.

Compare:

• en cuanto llegó = as soon as he arrived → no accent
• ¿cuánto cuesta? = how much does it cost? → accent, because it is interrogative

So the accent depends on the function of the word.

Because the sentence begins with a subordinate time clause:

• En cuanto terminó la grabación, = introductory clause
• empezamos la edición. = main clause

In Spanish, when this kind of clause comes first, a comma is normally used. It works similarly to English:

• As soon as the recording finished, we started editing.

If the main clause came first, the comma would often disappear:

• Empezamos la edición en cuanto terminó la grabación.

Yes. It depends on whether the action is viewed as completed/reported or still in the future.

In your sentence, the action happened in the past, so Spanish uses the indicative:

• En cuanto terminó la grabación, empezamos la edición.

But if you are talking about a future event, Spanish normally uses the subjunctive after en cuanto:

• En cuanto termine la grabación, empezaremos la edición.
• As soon as the recording finishes, we’ll start the editing.

So:

• past, real completed event → indicative
• future or pending event → subjunctive

Yes, depending on context.

Grabación can refer to:

• audio recording
• video recording
• filming/shooting

So if the wider context is music, it may mean recording.
If the context is film or TV, it may refer to filming or shooting.

Likewise, edición can mean editing audio, video, text, or another kind of material, depending on context.

You can use both.

• empezamos la edición
• comenzamos la edición

Both mean we started the editing.

In everyday Spanish, empezar is often a bit more common in conversation, while comenzar can sound slightly more formal or stylistically polished in some contexts. But both are perfectly correct.