Learn Hardcore Spanish (Spain): En casa hablamos de nuestros ingresos y de cada gasto importante. - At home we talk about our income and about each important expense.

The verb ending -amos in hablamos already tells you the subject is we (nosotros / nosotras), so the subject pronoun is usually omitted in Spanish.

(Nosotros) hablamos = we speak / we talk.

You only add nosotros for emphasis or contrast, for example:
En casa, nosotros hablamos de nuestros ingresos, pero ellos no hablan de dinero.

Could hablamos also mean we spoke (past tense) here?

Yes, in writing hablamos is the same form for:

present: we speak / we talk
preterite past: we spoke

Context normally makes it clear. In this sentence, talking about a regular practice at home, it is naturally understood as present (a habitual action): At home we talk about.... If you wanted to make it clearly past, you could add a time expression like Ayer en casa hablamos de....

Why do we say hablar de in hablamos de nuestros ingresos? Could we just say hablamos nuestros ingresos?

With the meaning to talk about something, Spanish normally uses hablar de (or hablar sobre), not the verb directly followed by a noun:

hablar de dinero = to talk about money
hablar de nuestros ingresos = to talk about our income

Hablamos nuestros ingresos sounds wrong; without de, hablar is usually used more like to speak a language (hablar español) or to speak with someone (hablar con mi jefe), not to speak about something.

Is there any difference between hablar de and hablar sobre?

In everyday use, hablar de and hablar sobre are very close in meaning: to talk about.

En casa hablamos de dinero.
En casa hablamos sobre dinero.

Both are fine. Sobre can sometimes sound a bit more formal or neutral; de is the most common and completely natural here.

Why is it nuestros ingresos and not nuestro ingreso?

The noun ingresos is normally used in the plural when talking about someone’s income or earnings in general. It can include salary, side jobs, interest, etc.

nuestros ingresos = our income / incomes, our earnings
Using nuestro ingreso (singular) is possible but less common; it would sound more like a single, specific inflow of money rather than your overall income situation.

Why is it nuestros ingresos and not nuestras ingresos?

The possessive nuestros / nuestras must agree with the gender and number of the thing owned, not the owners.

ingreso is masculine singular → el ingreso
ingresos is masculine plural → los ingresos

So you must say nuestros ingresos (masculine plural). Nuestras ingresos would be grammatically incorrect.

Why do we repeat de before cada gasto importante? Could we say …de nuestros ingresos y cada gasto importante?

You should repeat de here. Each part of the list depends on that preposition:

hablamos de nuestros ingresos
(hablamos) de cada gasto importante

Saying …de nuestros ingresos y cada gasto importante is understandable, but it sounds incomplete or a bit clumsy in careful Spanish. Repeating de makes the sentence clearer and more natural:
…de nuestros ingresos y de cada gasto importante.

Why is it cada gasto importante (singular) and not cada gastos importantes (plural)?

In Spanish, cada is always followed by a singular noun:

cada gasto = each expense
cada problema = each problem

So you say cada gasto importante, never cada gastos importantes. The idea of plurality (more than one expense) is already contained in cada.

What exactly does gasto mean here, and how is it different from pago, coste, or cuenta?

gasto = an expense, something you spend money on (the act or item that causes spending).
pago = a payment (the act of paying, or an individual payment).
coste / costo = cost (the price or economic cost of something); coste is more common in Spain.
cuenta = bill / account / check (at a restaurant, utility bill, bank account, etc.).

So cada gasto importante means each important expense – every significant thing on which money is spent.

Does En casa hablamos… mean this is a regular habit?

Yes. The present simple in Spanish is often used for habitual actions, just like in English:

En casa hablamos de nuestros ingresos… = At home we talk about our income… (as a regular practice)

So the sentence suggests this is something the family normally does, not just a one-time conversation.

Could I change the word order and say En casa hablamos de cada gasto importante y de nuestros ingresos?

Yes.

En casa hablamos de nuestros ingresos y de cada gasto importante.
En casa hablamos de cada gasto importante y de nuestros ingresos.

Both are grammatically correct and natural. You just slightly change which element you mention first; the meaning is essentially the same.