gaein samusireun bangeumi doeneun dedaga chaegwangdo johayo.

개인 사무실 means a private office or an individual office.

• 개인 = individual, personal, private
• 사무실 = office

So this refers to an office used by one person, as opposed to a shared office or open workspace.

은 is the topic marker. It sets 개인 사무실 as the thing being talked about.

So 개인 사무실은 ... is like:

• As for private offices, ...
• Private offices, ...

It can also give a slight contrastive feeling depending on context, especially if the speaker is comparing different office types.

방음이 되다 is a very common kind of Korean expression.

• 방음 = soundproofing, sound insulation
• 되다 = to become, to be done, to work, to be in place

So 방음이 되다 literally means something like soundproofing is done or soundproofing works, and in natural English it often means:

• to be soundproof
• to have sound insulation

The 이 is there because 방음 is treated as the subject of 되다.

This is similar to other common patterns such as:

• 준비가 되다 = to be ready / for preparation to be done
• 예약이 되다 = for a reservation to be made / to be reservable

So 방음이 되는 means that is soundproof or that has soundproofing.

-는 데다가 means besides that, on top of that, or and what's more.

It is used to add another point, often another advantage or reason in the same direction.

So here:

• 방음이 되는 데다가 채광도 좋아요
• It’s soundproof, and on top of that, the natural lighting is good too.

This grammar is often used when the speaker is listing multiple positive points, or multiple negative points.

Examples of the feeling:

• not only X, but also Y
• X, and on top of that, Y

Because 데다가 attaches to the adnominal form of the verb or adjective, not to the dictionary form.

So:

• dictionary form: 되다
• form used before 데다가 here: 되는

That is why you get:

• 방음이 되는 데다가 ...

not

• 방음이 되다 데다가

This is just how the grammar works. Before 데다가, Korean uses a form that links the clause smoothly to the next idea.

Yes, in standard spacing it is written as 되는 데다가.

• 되는 = the modifying form of 되다
• 데다가 = the grammatical expression meaning on top of that / besides

So they are written separately.

채광 means natural lighting or the amount/quality of daylight coming into a room.

It does not just mean general brightness. It specifically refers to how well a space gets light from outside, especially sunlight.

That is why 채광이 좋다 is a very common expression for:

• the room gets good natural light
• the lighting is good
• it’s bright with natural daylight

도 means also, too, or as well.

So 채광도 좋아요 means:

• the natural lighting is also good
• the lighting is good too

Here, 도 shows that this is an additional positive point after the first one:

• it is soundproof
• and also the natural lighting is good

A useful thing to notice is that 도 often replaces another particle.
So 채광도 좋아요 is understood like 채광이/은 좋아요, too.

Because 좋다 and 좋아하다 are different.

• 좋다 = to be good
• 좋아하다 = to like

In this sentence, the speaker is describing a quality of 채광:

• 채광이 좋아요 = the natural lighting is good

If you said 좋아해요, that would mean someone likes something, which does not fit here.

So:

• 채광이 좋아요 = correct
• 채광을 좋아해요 = would mean someone likes natural lighting

No. Korean often leaves out repeated subjects when they are already clear from context.

Here, 개인 사무실은 is the topic for the whole sentence, so both parts describe the same thing:

• 개인 사무실은 방음이 되는 데다가
• 개인 사무실은 채광도 좋아요

The second 개인 사무실은 is omitted because it would be unnecessary. This is very natural in Korean.