Learn Hardcore Indonesian: Apa pun rencana kamu, tolong beri kabar sebelumnya. - Whatever your plan is, please let me know beforehand.

Because pun is a particle that’s normally written separately from the word it follows. With question words, it makes “-ever” words: apa pun (whatever), siapa pun (whoever), kapan pun (whenever), di mana pun (wherever). In standard writing, keep it separate. The fused form apapun is very common informally but not recommended in formal contexts. Note: some fixed forms do fuse, e.g., walaupun, meskipun, bagaimanapun, adapun.

Is "Apa pun rencana kamu" okay without a verb like “is”?

Yes. Indonesian often omits a copula (“to be”). Apa pun rencana kamu, … literally means “Whatever your plan (is), …” and is perfectly grammatical. You’ll see similar frames like Apa pun alasannya, ….

What’s the difference between "rencana kamu" and "rencanamu"?

Both mean “your plan.” -mu is a clitic possessive that attaches to the noun: rencana + -mu → rencanamu.

rencanamu feels a bit smoother and is very common.
rencana kamu is also fine, slightly more explicit/casual.
Don’t write rencana mu with a space; attach -mu with no space.

Should I use "kamu", "Anda", or "kalian" here?

kamu: informal singular “you.”
Anda: polite/neutral singular “you” (capitalize the A).
kalian: plural “you (all).”
Examples: Apa pun rencana Anda, mohon beri kabar sebelumnya. / Apa pun rencana kalian, tolong beri kabar sebelumnya.

What does "tolong" do here?

tolong softens the imperative—roughly “please (help by).” It’s natural when asking someone to do something for you: Tolong beri kabar …. More formal options: mohon (humble) or harap (official tone). You can also soften with bisa: Bisa kabari saya sebelumnya?

What’s the nuance of "beri kabar" vs "beri tahu/beritahu/kasih tahu/kabari"?

beri kabar: “let (me/us) know; give a heads-up,” general notice.
beri tahu / beritahu: “tell/inform (with specifics).” Imperative Beritahu saya is common; beri tahu (two words) is also correct.
kasih tahu: colloquial “tell.”
kabari: “inform (someone)” (object marked by -i), e.g., Kabari saya.
All work; pick by register and whether you want general notice vs specific info.

Where do I put the object “me” with "beri kabar"?

Good options:

Beri kabar ke/kepada saya.
Beri saya kabar.
Kabari saya.
Avoid Beri kabar saya (that sounds like “give my news,” not “inform me”).

What exactly does "sebelumnya" mean here? Is it “in advance”?

Yes—here sebelumnya means “in advance / beforehand.” Synonyms: terlebih dahulu (more formal), lebih dulu/lebih dahulu, or casual dulu (often “first, before anything else”). Note that sentence-initial Sebelumnya, … can also mean “Previously, …” (referring to prior context).

Can I move "sebelumnya" elsewhere?

Yes. All are natural, with slight stylistic differences:

Tolong beri kabar sebelumnya.
Sebelumnya, tolong beri kabar. (a bit more formal/discourse-like)
Tolong kabari saya terlebih dahulu.
Tolong beri kabar dulu. (very everyday)

Is the comma after "Apa pun rencana kamu" necessary?

Recommended, yes. You’re fronting a concessive phrase (“Whatever your plan is, …”), so a comma helps mark the pause and improves readability. You’ll often see a comma in this structure.

How would I say this more formally or more casually?

Formal: Apa pun rencana Anda, mohon kabari kami terlebih dahulu.
Casual: Apa pun rencanamu, kabarin dulu ya.

Can I use "apa saja" instead of "apa pun"?

Not here. apa pun means “whatever” (no matter what it is). apa saja tends to mean “any/what things (plural or a set).” Rencanamu apa saja? asks “What are your plans (what items)?”—different meaning. Stick with apa pun for the concessive “whatever.”

Can I say "Apa pun yang rencana kamu"?

No. yang doesn’t link to a bare noun like that. Use either:

Apa pun rencanamu, …
Apa pun yang kamu rencanakan, … (here yang introduces a clause with a verb).