Eu vou misturar o café com leite agora.

Both are possible, but they imply different things:

• Eu vou misturar o café com leite agora. = I’m going to mix coffee with milk now (an intention / near-future action; very common in speech).
• Eu misturo o café com leite agora. = I mix / I’m mixing the coffee with milk now (can sound like a habitual instruction or a “right now, I do X” description; less natural here unless you’re narrating what you’re doing). In Brazilian Portuguese, ir + infinitive (vou misturar) is a very common way to talk about the near future.

Yes, vou is the present of ir (to go), but in Portuguese it’s also used as an auxiliary in ir + infinitive:

• vou + misturar = “I’m going to mix” This construction can indicate intention, decision, or immediate future—similar to English “going to,” but even more common in everyday Brazilian Portuguese.

Because misturar here is used as a normal transitive verb: you’re mixing one thing with another.

• misturar X com Y = to mix X with Y
  Reflexive forms like misturar-se exist, but mean something closer to “to mix in / mingle” (people mixing together, or something blending in), not the basic “mix coffee with milk” action.

They’re different structures:

• misturar o café com leite = mix the coffee with milk (combine them).
• misturar o café no leite can be heard, but it tends to suggest mixing coffee into the milk (focus on where it’s being mixed), and it’s less neutral. For a straightforward “coffee with milk,” com leite is the standard phrasing.

Portuguese often uses definite articles where English doesn’t, especially with specific items in context:

• o café can mean “the coffee” (the coffee you’re dealing with right now). If you said Eu vou misturar café com leite agora, it sounds more like you’re talking about coffee in general or the drink as a category, not necessarily a specific cup/pot.

Yes. misturar X ao Y is also correct and fairly common:

• misturar o café ao leite = mix the coffee with/into the milk
  In practice:
• com is very common and neutral.
• a + o = ao can sound a bit more “formal” or recipe-like, depending on context.

Yes, café com leite is a very common set phrase meaning “coffee with milk.” People often use it as the name of the drink:

• Quero um café com leite. = “I want a coffee with milk.” In your sentence, it’s still literal (you’re combining them), but it also echoes that common drink name.

It’s flexible. These all work with slightly different emphasis:

• Eu vou misturar o café com leite agora. (neutral)
• Agora eu vou misturar o café com leite. (emphasizes “now”)
• Eu vou agora misturar o café com leite. (possible, but often feels a bit marked; more common in writing or for emphasis) End position is very natural in speech.

Yes. Portuguese is often “pro-drop” (the subject can be omitted) because the verb form already shows who it is:

• Vou misturar o café com leite agora. = very common and natural.

Approximate guides (Brazilian Portuguese):

• vou ≈ “voh” (often like /vo(w)/, with a slight glide at the end).
• com has a nasal ending: it’s not a full “m” sound like English. It’s closer to “kõ” (like /kõ/), with nasalization on the vowel.