Ensayamos la escaleta antes de difundir la cabecera.

It can be either, because ensayamos is the same form for:

• present: we rehearse / we are rehearsing
• preterite: we rehearsed

So, taken by itself, the sentence is ambiguous. Context tells you which meaning is intended.

For example:

• In a general workflow description, it would probably be present.
• In a narration of completed events, it would probably be preterite.

This is very common with -ar verbs in nosotros in Spanish.

After antes, Spanish normally uses:

• antes de + infinitive
  when the subject is the same, or when the subject is not being stated explicitly

So antes de difundir la cabecera means before broadcasting/publishing the opening/header.

If Spanish wants to introduce a new conjugated verb with its own subject, it uses:

• antes de que + subjunctive

Example:

• Ensayamos la escaleta antes de difundir la cabecera.
  We rehearse/rehearsed the rundown before broadcasting the opening.

• Ensayamos la escaleta antes de que empiece el programa.
  We rehearse/rehearsed the rundown before the programme starts/started.

So in your sentence, difundir stays in the infinitive because that is the normal structure after antes de.

In Spain, escaleta is a very common media/production term. It usually means something like:

• a rundown
• a running order
• a programme outline
• a scene-by-scene or segment-by-segment plan

It is especially used in:

• television
• radio
• audiovisual production
• sometimes theatre or events

So it is not just any random outline; it often suggests a structured sequence of parts in a production.

Cabecera has several meanings in Spanish, so learners often pause at this word.

In media contexts in Spain, it can mean things like:

• the opening title sequence
• the intro
• the programme opening
• sometimes the masthead/header/nameplate, depending on the medium

In this sentence, because it goes with difundir, it most likely refers to some kind of opening/intro segment or another media element that is going to be released, aired, or published.

So the exact English word depends on the situation, but the Spanish word itself is very natural in media language.

Because both nouns are being treated as specific, known things.

• la escaleta = the particular rundown/outline we are working with
• la cabecera = the particular opening/header we are going to release or air

Spanish often uses the definite article where English also would, especially when referring to something concrete and already identifiable in context.

If you removed the articles, the sentence would sound unnatural here.

Because Spanish usually drops subject pronouns when the verb already shows who the subject is.

• Ensayamos already tells you the subject is we

So:

• Ensayamos la escaleta... = normal, neutral
• Nosotros ensayamos la escaleta... = possible, but more emphatic or contrastive

You would add nosotros only if you wanted to stress something like:

• We rehearsed it, not them.
• We, at least, did our part.

Yes, but its exact English equivalent changes with context.

Difundir is a broad verb meaning things like:

• to disseminate
• to spread
• to broadcast
• to publish
• to release

In media language, it can sound slightly more formal or institutional than some other verbs.

Compare:

• difundir = to disseminate / broadcast / release
• emitir = to air / broadcast
• publicar = to publish
• lanzar = to launch / release

So difundir la cabecera is possible if the idea is that the intro/opening/header is being made public or broadcast. Depending on the exact context, another verb might also be possible, but difundir is not wrong.

Yes, absolutely. That version is perfectly natural.

Both orders work:

• Ensayamos la escaleta antes de difundir la cabecera.
• Antes de difundir la cabecera, ensayamos la escaleta.

The difference is mainly focus:

• putting antes de difundir la cabecera first highlights the timing or sequence
• putting it second sounds a bit more neutral

Spanish is flexible with this kind of word order.

It is understandable and can be natural in a production context, especially if the idea is that the team is rehearsing according to the rundown.

That said, depending on the exact nuance, Spanish speakers might also say:

• repasar la escaleta = go over the rundown
• revisar la escaleta = review the rundown
• seguir la escaleta = follow the rundown

So:

• ensayar la escaleta suggests a more active rehearsal
• repasar/revisar la escaleta suggests checking or reviewing it

Your sentence sounds like a production team rehearsing before something goes out.

It sounds strongly like a media, broadcasting, or production context, especially in Spain.

The clues are:

• escaleta = rundown / running order
• cabecera = opening sequence / header / masthead
• difundir = broadcast / publish / release

So a native speaker would probably imagine something involving:

• a TV programme
• a radio show
• a news or audiovisual production team
• possibly a digital media workflow

Without context, the sentence is a little technical, but within media Spanish it is quite plausible.