Learn Hardcore Indonesian: Kami bekerja seharian, tetapi istirahat sebentar sebelum pulang. - We worked all day, but took a short break before going home.

So kami implies the speaker’s group worked, but the person being addressed was not part of that group. If you are talking to teammates who also worked, use kita.

Do I need to repeat the subject in the second clause (before istirahat)?

No. Indonesian often drops the repeated subject when it’s the same as in the previous clause. All are acceptable:

Kami bekerja seharian, tetapi istirahat sebentar sebelum pulang. (natural, concise)
Kami bekerja seharian, tetapi kami beristirahat sebentar sebelum pulang. (also correct; heavier, adds emphasis/clarity)

Should it be istirahat or beristirahat?

Both are correct. Istirahat can function as a verb (to rest) or a noun (a rest). Beristirahat is the more overtly verbal/standard form and feels a bit more formal. In everyday speech and writing, istirahat on its own is very common:

Kami istirahat sebentar. (very common)
Kami beristirahat sebentar. (a bit more formal)

What exactly does sebentar mean? Are there alternatives?

Sebentar means for a short while, briefly, a moment. Common variants:

sebentar saja = just for a moment
sejenak = for a moment (slightly more literary)
bentar = colloquial/clipped form (informal) Also note: sebentar lagi means in a moment/soon.

What does seharian mean, and how is it different from sehari, sehari-hari, and sepanjang hari?

seharian = all day long, for the whole day (duration)
sehari = one day/a day (quantity)
sehari-hari = daily/every day (habit)
sepanjang hari = all day long (synonym of seharian, a bit more neutral/formal) Examples:
Kami bekerja seharian.
Saya libur sehari.
Saya berolahraga sehari-hari.
Kami bekerja sepanjang hari.

Can seharian go in a different position?

Yes. Both are natural, with slightly different emphasis:

Kami bekerja seharian. (focus on the action; duration at the end)
Kami seharian bekerja. (light emphasis on the duration up front) You can also say seharian penuh to stress the completeness: all day long, fully.

Does the sentence mean past, present, or habitual? Indonesian has no tense marking here.

Without time markers, it’s ambiguous and depends on context. You can disambiguate:

Past: Tadi kami bekerja seharian, tetapi istirahat sebentar sebelum pulang. / Kami sudah bekerja seharian…
Present progressive: Kami sedang bekerja seharian… (less common; usually context suffices)
Future: Besok kami akan bekerja seharian, lalu istirahat sebentar sebelum pulang. Indonesian relies on time words like tadi, kemarin, besok, or particles like sudah, akan, sedang.

Why use tetapi here? Could I use dan, lalu, or kemudian instead?

tetapi = but/however (introduces contrast or an unexpected twist)
dan = and (just adds another action)
lalu/kemudian = then/after that (emphasizes sequence) If you want simple sequence rather than contrast, dan or lalu/kemudian is more straightforward:
Kami bekerja seharian, lalu istirahat sebentar sebelum pulang. With tetapi, the nuance is we worked all day, but still took a short break (slight contrast with the expectation of nonstop work).

What’s the difference between tetapi, tapi, and namun?

tetapi = neutral to formal; good in writing and speech.
tapi = informal/spoken.
namun = however; typically used at the start of a sentence or clause as a sentence connector. Examples:
Kami bekerja seharian, tetapi istirahat sebentar… (neutral)
Kami bekerja seharian, tapi istirahat sebentar… (casual)
Kami bekerja seharian. Namun, kami istirahat sebentar… (more formal/discoursal)

Is the comma before tetapi required?

Recommended. In standard punctuation, place a comma before tetapi when it connects two independent clauses:

Kami bekerja seharian, tetapi istirahat sebentar sebelum pulang.

Why is it sebelum pulang and not sebelum pergi pulang or sebelum pulang ke rumah?

Pulang already means go home/return home, so you don’t need pergi or ke rumah. Pulang ke rumah is possible but redundant unless you want to emphasize home explicitly. In casual speech, some might use balik (go back) instead of pulang:

sebelum pulang (standard)
sebelum balik (informal)
sebelum kembali is more like before returning (to a place), less specifically home.

Should it be sebelum pulang or sebelum kami pulang?

If the subject of both clauses is the same, you can omit it:

… sebelum pulang. (= before we went home) If the subject differs, specify it:
… sebelum dia pulang. (= before he/she went home) Adding kami is also fine for clarity: … sebelum kami pulang.

Can I reword the sentence to highlight sequence rather than contrast?

Yes. Two natural options:

Move the time clause: Sebelum pulang, kami istirahat sebentar.
Use setelah: Setelah bekerja seharian, kami istirahat sebentar sebelum pulang. These versions emphasize chronology without a contrastive tetapi.

What does the prefix ber- do in bekerja, and how does that differ from mengerjakan/kerjakan?

ber- typically forms intransitive verbs. Bekerja (from root kerja) means to work (do one’s job), intransitively. Mengerjakan is transitive: to do/work on something (a task). Kerjakan is the imperative form of mengerjakan.

Saya bekerja di kantor. (I work at an office.)
Saya mengerjakan tugas. (I’m doing a task/assignment.)
Kerjakan PR-mu! (Do your homework!)