Learn Hardcore Greek: Πότε θέλετε να πάμε;

for addressing more than one person (you all)
as a polite form to one person (like French vous) Informal singular is θέλεις: Πότε θέλεις να πάμε;

Why do we need να? Can I say Πότε θέλετε πάμε;?

You need να. Verbs of wanting/trying/being able (e.g., θέλω, προσπαθώ, μπορώ) normally take a να-clause. So: Πότε θέλετε να πάμε; is correct; dropping να is ungrammatical here.

What form is πάμε here? Is it the same as “let’s go”?

It’s 1st person plural in a να-clause (subjunctive). Formally it’s the perfective (aorist) subjunctive: “for us to go (once).”

With να: να πάμε = for us to go.
On its own as an exclamation, Πάμε! = Let’s go! (hortative use of the same form).

How would I make this informal with singular “you”?

Use θέλεις: Πότε θέλεις να πάμε;