Learn Hardcore Portuguese (Brazil): Eu vou conversar com ela amanhã.

Yes. Vou conversar com ela amanhã. is perfectly natural because vou clearly marks first person singular. Keep Eu if you want emphasis or contrast, e.g., Eu vou conversar com ela, não você.

Why is it vou conversar instead of conversarei?

Brazilian Portuguese strongly prefers the periphrastic future (ir + infinitive) in speech: Eu vou conversar… It’s neutral and very common.

Conversarei (synthetic future) sounds formal or literary in Brazil.
Irei conversar is also possible, a bit more formal or emphatic about intention.
All three mean “I will talk,” but vou conversar is the go-to in everyday speech.

What’s the difference between conversar, falar, and dizer?

conversar (com) = to have a conversation with (two-way exchange). Example: Vou conversar com ela.
falar (com/para/a) = to talk/speak. With com it’s like “talk with”; with para/a it’s “talk to/tell” (one-way). Example: Vou falar com ela ≈ “talk with her”; Vou falar para ela ≈ “tell her.”
dizer (a/para) = to say/tell (more direct). Example: Vou dizer a ela/para ela.
In your sentence, conversar com emphasizes an actual conversation.

Why is it com and not para or a?

com = with, implies a two-way conversation: conversar/falar com alguém.
para/a = to, usually one-way delivery of information: falar para/a alguém, dizer a/para alguém.
So for “have a talk with her,” com is the natural choice: conversar com ela.

Why com ela and not com a ela?

With pronouns, you use the preposition alone: com ela, com ele, com eles/elas. You don’t add the article. Com a ela is incorrect.
Articles appear with nouns: com a Maria, com o João.

If I replace ela with a name, do I need the article?

Both are heard in Brazil, depending on region and style:

Vou conversar com a Maria amanhã. (very common)
Vou conversar com Maria amanhã. (also fine)
Using the article with personal names is widespread in Brazilian Portuguese; either form is generally acceptable.

Where can I put amanhã in the sentence?

Common options:

Vou conversar com ela amanhã. (most typical)
Amanhã vou conversar com ela.
Amanhã eu vou conversar com ela.
If amanhã comes first, a comma is optional (and often omitted when it’s a single word).

How do I negate this?

Place não before the conjugated verb: Eu não vou conversar com ela amanhã.
Don’t say: Eu vou não conversar…

How do I turn it into a question?

Use rising intonation and (optionally) add a subject:

Vai conversar com ela amanhã?
Você vai conversar com ela amanhã?
For wh-questions: Quando você vai conversar com ela? / Com quem você vai conversar amanhã?

Can I use the simple present for a planned future?

Yes. Amanhã eu converso com ela. is common for scheduled/expected future actions, similar to English “I talk to her tomorrow” in context.

Can I say vou conversá-la?

No. Conversar takes com (it’s not a direct-object verb), so you can’t attach a direct-object clitic. Say vou conversar com ela.
Similarly, avoid falá-la for “talk to her”; use falar com ela. For “tell her,” you can use dizer a/para ela or the clitic in formal style (vou lhe dizer).

If I’m speaking to the person directly, do I still use ela?

No. Use você (or polite a senhora/o senhor) when addressing someone: Eu vou conversar com você amanhã.
Use ela only when referring to a third person.

Are there special forms with com like comigo?

Yes:

comigo (with me), contigo (with you – tu), consigo (with him/her/you-formal; rare/ambiguous in Brazil), conosco (with us).
Third person usually stays regular: com ele/ela/eles/elas. In everyday Brazilian Portuguese, com você/vocês and com a gente are very common.

Any quick pronunciation tips for this sentence?

eu: glides to something like “eh-oo,” often very quick.
vou: “voh” (closed “o”).
conversar: stress the last syllable: con-ver-SAR; final r often sounds like a soft “h” in Brazil.
com: nasal “õ,” like “kohng.”
ela: “EH-lah.”
amanhã: “ah-ma-NYAN”; nh like “ny” in “canyon,” and ã is nasal.