Hoe langer ik aan mijn scriptie werk, des te belangrijker wordt een rustige werkplek.

It is a correlative comparative pattern, equivalent to English the longer ..., the more important ....

So:

• Hoe langer ik aan mijn scriptie werk = The longer I work on my thesis
• des te belangrijker wordt een rustige werkplek = the more important a quiet workspace becomes

A useful way to remember it is:

• hoe + comparative, des te + comparative
• English: the + comparative, the + comparative

Examples:

• Hoe ouder je wordt, des te wijzer je wordt.
  The older you get, the wiser you become.
• Hoe meer ik oefen, des te beter ik speel.
  The more I practise, the better I play.

Because in this sentence hoe is not asking a question. It is part of a fixed comparative structure.

So here hoe langer does not mean how long(er). It means something like:

• the longer
• as ... more and more

This is one of those places where Dutch hoe and English how are related historically, but the exact use is different.

Compare:

• Hoe lang werk je aan je scriptie? = How long have you been working on your thesis?
  → real question

• Hoe langer ik aan mijn scriptie werk, des te belangrijker wordt een rustige werkplek.
  → not a question, but a comparison of increasing degree

Des te introduces the second half of the comparison: the more / the less.

So:

• hoe langer = the longer
• des te belangrijker = the more important

In modern Dutch, des te sounds a bit more formal or written than some other options, but it is very normal and correct.

You may also encounter:

• Hoe langer ik aan mijn scriptie werk, hoe belangrijker een rustige werkplek wordt.

That version is also correct and often feels a bit more everyday. The meaning is the same.

Because both are comparatives.

• lang = long

• langer = longer

• belangrijk = important
• belangrijker = more important

The whole sentence compares two changing things:

• as the time spent working gets longer
• a quiet workspace becomes more important

That is why Dutch uses the comparative in both halves of the structure.

Because the verb is werken aan = to work on.

So in Dutch, aan belongs with the verb:

• aan een project werken = to work on a project
• aan een boek werken = to work on a book
• aan mijn scriptie werken = to work on my thesis

This is a fixed prepositional pattern, and English speakers simply have to learn it as part of the verb.

So:

• Ik werk aan mijn scriptie. = I am working on my thesis.

Scriptie usually means a substantial academic paper or thesis, especially at university level.

Depending on context, it can be translated as:

• thesis
• dissertation
• research paper

In many everyday learner contexts, thesis is the safest translation.

So:

• mijn scriptie = my thesis

Because Dutch main clauses normally use verb-second word order.

The element des te belangrijker comes first in the second clause, so the finite verb must come next:

• des te belangrijker = first position
• wordt = second position
• een rustige werkplek = subject comes after the verb

So the structure is:

• Des te belangrijker wordt een rustige werkplek.

Not:

• Des te belangrijker een rustige werkplek wordt.
  That would sound wrong in this independent clause.

A more literal breakdown is:

• The more important becomes a quiet workspace

That sounds odd in English, but it is normal Dutch word order.

Because the idea is becoming more important, not simply being important.

• is belangrijk = is important
• wordt belangrijker = becomes more important

This fits the gradual change expressed by hoe ..., des te ....

The sentence is saying that as time goes on, the importance of a quiet workspace increases. So wordt is a very natural choice.

It is the subject, but Dutch allows the subject to come after the verb when something else is placed first.

In the second clause:

• des te belangrijker is placed first for emphasis and because it matches the comparative structure
• then comes the finite verb wordt
• then the subject een rustige werkplek

This is a normal inversion pattern in Dutch.

You can compare:

• Een rustige werkplek wordt belangrijker.
  neutral order

• Des te belangrijker wordt een rustige werkplek.
  comparative structure, so inversion happens

Yes. That is a very common alternative.

So this sentence can also be said as:

• Hoe langer ik aan mijn scriptie werk, hoe belangrijker een rustige werkplek wordt.

This means the same thing.

A rough difference in feel:

• hoe ..., des te ... = slightly more formal, polished, or written
• hoe ..., hoe ... = very common and often a bit more conversational

Both are correct Dutch.

Yes, the comma is standard here.

The sentence has two linked parts:

• Hoe langer ik aan mijn scriptie werk
• des te belangrijker wordt een rustige werkplek

Dutch normally separates these parts with a comma in this kind of comparative construction.

So the punctuation in the original sentence is correct and natural.

Yes, very often. It is a productive pattern in Dutch.

Common models:

• Hoe meer ..., des te beter ...
  The more ..., the better ...

• Hoe minder ..., des te moeilijker ...
  The less ..., the more difficult ...

• Hoe vaker ..., des te gemakkelijker ...
  The more often ..., the easier ...

Examples:

• Hoe meer je leest, des te groter je woordenschat wordt.
  The more you read, the larger your vocabulary becomes.

• Hoe langer we wachten, des te duurder het wordt.
  The longer we wait, the more expensive it becomes.

So the sentence you were given is a very useful model to learn from.