Learn Hardcore Indonesian: Kami pasti bertemu tatap muka besok, kecuali cuaca buruk. - We will surely meet face-to-face tomorrow, unless the weather is bad.

kami = we (excluding the person you’re speaking to).
kita = we (including the person you’re speaking to).
Using kami implies you’re telling a third party about a meeting that doesn’t include them. If you’re speaking to the person you’ll meet, say: Kita pasti bertemu tatap muka besok...

Do I need akan to talk about the future?

No. besok already marks the future.

Natural: Kami pasti bertemu besok...
Also fine (a bit heavier/more formal): Kami pasti akan bertemu besok...
Order tip: say pasti akan, not akan pasti.

Where should pasti go?

Default: before the verb phrase: Kami pasti bertemu...
Emphatic (sentence-initial): Pasti kami bertemu...
After the verb sounds odd: Kami bertemu pasti... is unnatural.

Is bertemu tatap muka redundant? Doesn’t bertemu already imply in person?

Not necessarily. Today bertemu can be in person or online. tatap muka clarifies it’s in-person.
Good alternatives:

Kami pasti bertatap muka besok.
Kami pasti bertemu langsung besok.

Can I use ketemu?

Yes, but it’s colloquial. Use it in casual speech/text: Kita pasti ketemu besok...
For formal writing, prefer bertemu or bertatap muka.

Do I need dengan after bertemu?

Both are common:

bertemu [person]: Saya bertemu dia kemarin.
bertemu dengan [person]: Saya bertemu dengan dia kemarin.
If you specifically “go to meet/see” someone, use menemui [person].

Is kecuali cuaca buruk okay without kalau/jika?

Yes. It’s an accepted ellipsis meaning “unless [there is] bad weather.”
More explicit variants: kecuali kalau cuacanya buruk / kecuali jika cuacanya buruk. All are correct.

Should it be cuaca buruk or cuacanya buruk?

cuaca buruk = “bad weather” (general).
cuacanya buruk = “the weather is bad” (more specific/definite for that time).
Both work here; cuacanya feels a bit more definite.

Is the comma before kecuali required?

It’s recommended but not mandatory. A comma helps readability because kecuali... introduces an exception/condition.

Can I start with the exception?

Yes: Kecuali cuaca buruk, kami pasti bertemu tatap muka besok.
This front-loads the caveat and is perfectly natural.

What’s the difference between besok, esok, lusa, and nanti?

besok = tomorrow (neutral/common).
esok = tomorrow (more formal/literary; common in news and Malay).
lusa = the day after tomorrow.
nanti = later (not necessarily tomorrow).

How do I spell tatap muka? Is a hyphen used?

Standard spelling is two words: tatap muka.
As a verb with the prefix, it’s one word: bertatap muka.
Hyphenated tatap-muka is nonstandard.

Is bertemu muka good Indonesian?

You might see it, but the common/idiomatic expression today is bertatap muka or the adverbial tatap muka. Prefer those.

What’s the difference between pasti tidak and tidak pasti?

pasti tidak = definitely not (certainty about a negative).
tidak pasti = not certain/uncertain.
Example: Kami pasti tidak bertemu = We definitely won’t meet.
Pertemuan besok tidak pasti = Tomorrow’s meeting is uncertain.

Does kecuali mean both “except (for)” and “unless”?

Yes.

“Except (for)” with nouns: Semua datang kecuali Rina (Everyone came except Rina).
“Unless” with conditions: Kami bertemu besok, kecuali (kalau) cuaca buruk.

How else could I naturally say the whole sentence?

Kalau cuacanya buruk, kami tidak jadi bertemu tatap muka besok.
Kami pasti akan bertatap muka besok, kecuali kalau hujan deras.
Casual and inclusive: Kita pasti ketemu langsung besok, kecuali cuacanya jelek.