Learn Hardcore German: Häufige Pausen helfen mir, im Großraumbüro ruhig zu bleiben. - Frequent breaks help me stay calm in the open-plan office.

jemandem helfen = to help someone (dative)
So mir (dative of ich) is correct, not mich (accusative).
Examples:
Er hilft mir.
Kannst du mir helfen?

Why does the sentence start with Häufige Pausen instead of Mir helfen häufige Pausen?

German often puts what you’re talking about (the topic) first. Here, Häufige Pausen is the subject and is placed in position 1 for emphasis/topic.
The key rule is: the finite verb (here helfen) stays in position 2 in a main clause. So:

Häufige Pausen (position 1) + helfen (position 2) + mir …

You could also say:

Mir helfen häufige Pausen, im Großraumbüro ruhig zu bleiben.
That changes the emphasis (more focus on mir).

Why is there a comma before im Großraumbüro ruhig zu bleiben?

Because im Großraumbüro ruhig zu bleiben is a zu-infinitive clause (an infinitive phrase with zu). German often uses a comma to separate these, especially when the phrase is longer or has its own elements (like im Großraumbüro).
In many cases, the comma is optional with simple infinitive phrases, but here it’s very common and clear.

What exactly is im Großraumbüro grammatically?

im is a contraction of in dem:

in + dem = im

Großraumbüro is neuter (das Großraumbüro), so dem is dative neuter.
Because this is a location (not motion), German uses dative with in:

in dem Großraumbüro → im Großraumbüro

Why is it zu bleiben? Could it be without zu?

After many verbs, German uses an infinitive with zu (similar in function to English to + verb). Here it’s:

helfen + (jemandem) + zu + infinitive

So: helfen mir, ruhig zu bleiben = help me to stay calm.
Without zu would be ungrammatical here (… ruhig bleiben).
(Contrast: modal verbs don’t use zu: Ich kann ruhig bleiben.)

Why is ruhig not declined (no adjective ending)?

Because ruhig here is not an adjective directly describing a noun; it’s an adverb/predicative complement describing the state of the subject (I). In structures like ruhig bleiben (to stay calm), the adjective stays in its base form:

ruhig bleiben
krank werden
müde sein

Adjective endings appear when the adjective is before a noun:

ein ruhiger Mensch (declined adjective)

Why is it Häufige Pausen (with -e)?

Because Pausen is plural (die Pause → die Pausen), and in the plural with no article, adjectives typically take -e (strong declension, nominative plural):

häufige Pausen
lange Meetings
kurze Nachrichten

Also, Häufige Pausen is the subject (nominative plural), matching helfen (plural verb form).

What does Großraumbüro mean, and how is that word built?

It’s a compound noun: Großraum + Büro.

groß = large
Raum = room/space
Büro = office

So Großraumbüro is an open-plan office (a large shared office space). The plural would be Großraumbüros.

Why is bleiben at the very end of the sentence?

Because zu-infinitive clauses put the infinitive verb at the end, and the rest of the phrase comes before it:

ruhig zu bleiben
besser zu schlafen
pünktlich anzukommen

German often “parks” non-finite verbs (infinitives/participles) at the end of their clause.

Could I also say um … zu bleiben here?

Not with the same meaning. um … zu expresses purpose (in order to). This sentence is not describing a goal but what the breaks help you do.
Correct here is simply the zu-infinitive after helfen:

… helfen mir, ruhig zu bleiben.

If you wanted a purpose structure, you’d need a different main verb/meaning, e.g.:

Ich mache häufig Pausen, um im Großraumbüro ruhig zu bleiben. (I take frequent breaks in order to stay calm.)

Is Häufige Pausen the same as oft Pausen?

Not exactly in form and style:

häufige Pausen = frequent breaks (noun phrase; sounds neutral/formal)
oft Pausen (machen) would usually need a verb to be complete, e.g. Ich mache oft Pausen. (I often take breaks.)

In your sentence, the subject is a noun phrase, so Häufige Pausen fits naturally.