Die soekgebied is so groot dat ons moet saamwerk.

Yes. Die here is the definite article, so it means the.

• die soekgebied = the search area
• Afrikaans uses die for all genders and for both singular and plural definite nouns.

So unlike languages that have different words for masculine/feminine/neuter, Afrikaans keeps it simple: just die.

Because Afrikaans very often forms compound nouns as one word.

Here:

• soek = search
• gebied = area

So soekgebied literally combines into search area.

This is very normal in Afrikaans. English often writes similar ideas as two words, but Afrikaans prefers one compound word:

• soekgebied
• huisdeur
• tafeldoek

If you are used to English spelling, this is something you will notice a lot in Afrikaans.

so ... dat ... is a very common Afrikaans structure meaning so ... that ...

So:

• so groot = so big / so large
• dat = that

Together:

• so groot dat ons moet saamwerk = so big that we have to work together

This pattern shows result:

• something is so much that a consequence follows.

A few similar examples:

• Dit is so warm dat ek nie kan slaap nie.
  = It is so hot that I cannot sleep.
• Hy is so moeg dat hy vroeg gaan slaap.
  = He is so tired that he goes to bed early.

Because so ... dat ... is a fixed comparison/result pattern.

• baie groot means very big
• so groot dat ... means so big that ...

So if you want the idea of result/consequence, use so:

• Die soekgebied is so groot dat ons moet saamwerk.

If you only want to say very big, without the that-clause, then baie is natural:

• Die soekgebied is baie groot.

So baie intensifies, but so ... dat creates a cause-and-result structure.

They are different words.

• so = so, like this, in this way
• soos = like / as

In your sentence, so is part of so ... dat ... = so ... that ...

Compare:

• Dit is so groot. = It is so big.
• Dit lyk soos 'n kaart. = It looks like a map.

So in this sentence, soos would be wrong.

No change is needed here. After a linking verb like is, Afrikaans adjectives normally stay in their basic form.

So:

• Die soekgebied is groot.
• Die gebied is moeilik.
• Die plan is goed.

This is called predicative use of the adjective: the adjective comes after is and describes the noun.

That is why you get:

• is so groot

and not some changed form.

Because dat introduces a subordinate clause.

In Afrikaans, subordinate clauses often push the verb group toward the end. In this short clause, there is not much material between the subject and the verbs, so it looks quite close to English:

• dat ons moet saamwerk

But if you add more words, the pattern becomes easier to see:

• dat ons nou beter moet saamwerk
• dat ons as 'n span moet saamwerk

The important part is that after dat, the clause follows subordinate-clause word order, not normal main-clause order.

Compare:

• Main clause: Ons moet saamwerk.
• After dat: ... dat ons moet saamwerk.

Because this clause is short, the difference is not dramatic, but the structure is still subordinate.

It can often mean either must or have to, depending on context.

In this sentence, moet expresses necessity:

• ons moet saamwerk = we must work together / we have to work together

Afrikaans moet is very common and covers both ideas in many situations. English may choose must or have to depending on tone, but Afrikaans often just uses moet.

Good question. Both forms are related.

saamwerk is the verb to work together / cooperate.

In Afrikaans, some verbs can appear:

• as a single word in the infinitive or after a modal
• as a split form when the verb is conjugated in a main clause

So:

• Ons moet saamwerk.
  Here it stays together because it comes after moet.

But:

• Ons werk saam.
  Here the finite verb is werk, and saam appears separately.

This is a very common Afrikaans pattern.

So in your sentence, saamwerk is one word because it is the infinitive after moet.

Normally, no.

Afrikaans generally uses fewer commas than English, and in a sentence like this, you would usually write:

• Die soekgebied is so groot dat ons moet saamwerk.

So the version without a comma is standard and natural.

Yes, absolutely. That is a very natural alternative.

• Die soekgebied is so groot dat ons moet saamwerk.
• Ons moet saamwerk omdat die soekgebied so groot is.

Both are correct and very close in meaning.

The difference is mainly focus:

• Die soekgebied is so groot dat ... emphasizes the size/result
• Ons moet saamwerk omdat ... emphasizes the need to work together first

Also notice that in the omdat clause, the verb is goes to the end:

• omdat die soekgebied so groot is

That is another common subordinate-clause pattern in Afrikaans.