Learn Hardcore Spanish (Spain): Miro el saldo de mi cuenta cada semana para controlar mis gastos. - I look at the balance of my account every week to control my expenses.

When you look at your account balance, you do it intentionally, so Spanish uses mirar:
Miro el saldo de mi cuenta… = I look at / check the balance of my account…

Using veo el saldo would sound odd, as if the balance just appears in front of you without you actively checking it.

Could I say Yo miro el saldo de mi cuenta…, or is yo wrong here?

You can say Yo miro el saldo de mi cuenta…, but in normal, neutral speech in Spanish (especially in Spain) the subject pronoun is usually omitted:

Miro el saldo de mi cuenta… (most natural)
Yo miro el saldo de mi cuenta… (correct, but adds emphasis on I)

Using yo here would sound like you’re contrasting yourself with someone else, e.g. Yo miro el saldo, pero mi hermano no.

In English we say “look at the balance”. Why is there no preposition after miro (not miro a el saldo)?

In Spanish, mirar is normally a direct transitive verb: it takes a direct object without a preposition.

Miro el saldo. = I look at the balance.
Miro la tele. = I watch TV.
Miro el reloj. = I look at the clock.

You only add a after mirar when you have a personal a (a person as direct object), e.g. Miro a mi hijo.
Since el saldo is a thing, you just say Miro el saldo (no a).

What exactly does saldo mean here, and is it masculine or feminine?

Saldo is masculine: el saldo.

In this context it means (account) balance, i.e. the amount of money in an account at a given moment. Common uses:

el saldo de mi cuenta – the balance of my (bank) account
el saldo de la tarjeta – the card balance
el saldo del teléfono – phone credit / balance (prepaid)

It’s different from English “balance” as a loanword; in everyday banking Spanish, saldo is the normal word.

Why is it el saldo de mi cuenta instead of simply mi saldo?

Both are possible, but they’re not identical in feel:

Miro mi saldo cada semana. – I look at my balance every week.
(Shorter, but a bit vague about what kind of balance.)
Miro el saldo de mi cuenta… – I look at the balance of my account…
(More specific and typical for bank language.)

El saldo de mi cuenta makes it very clear you mean your bank account balance, not, for example, your phone credit or some other “balance” you might have.

Why do we say el saldo de mi cuenta and not el saldo en mi cuenta?

Spanish normally expresses this relationship with de, not en:

el saldo de mi cuenta = the balance of my account
el número de mi cuenta = the number of my account

You would use en when talking about where the money is:

En mi cuenta hay 500 euros. – There are 500 euros in my account.

So:
saldo de mi cuenta (balance of my account)
but
dinero en mi cuenta (money in my account).

What does cada semana mean exactly? Is it the same as todas las semanas?

Cada semana literally means each week.
Todas las semanas literally means every week / all the weeks.

In most everyday contexts, they are practically interchangeable:

Miro el saldo cada semana.
Miro el saldo todas las semanas.

Both mean you do it once every week on a regular basis.
If anything, cada semana can feel slightly more neutral and regular, but the difference is very small here.

Can I move cada semana to other positions in the sentence?

Yes. All of these are correct, with only slight differences in emphasis:

Miro el saldo de mi cuenta cada semana para controlar mis gastos.
(Very natural; time expression in the middle.)
Cada semana miro el saldo de mi cuenta para controlar mis gastos.
(Emphasis a bit more on the frequency: Every week I…)
Miro el saldo de mi cuenta para controlar mis gastos cada semana.
(Grammatically OK, but can sound slightly heavier; context decides if it’s natural.)

Most commonly you’ll hear it either at the beginning or just after the verb phrase, as in the original sentence.

Why is it para controlar and not por controlar mis gastos?

Para is used to express purpose / goal – in order to:

Miro el saldo… para controlar mis gastos.
= I look at the balance in order to keep track of my expenses.

Por would usually express cause, reason, or exchange, and doesn’t fit here.
So for “I do X in order to Y”, Spanish uses para + infinitive, not por:

Estudio español para viajar a España.
Trabajo para ganar dinero.

Does controlar here mean “to control” like to have power over something?

Not exactly. Controlar is a common false friend.

In Spain, in everyday language, controlar often means:

to check, to monitor, to keep an eye on, to keep track of

So:

controlar mis gastos ≈ to monitor/keep track of my expenses,
not “to dominate my expenses” in a power sense.

You can use controlar in the stronger sense of “to control”, but here it’s clearly the softer “keep under observation” meaning.

Why is it mis gastos and not just los gastos?

Mis gastos means my expenses – it clearly refers to your own spending.

Miro el saldo… para controlar mis gastos.
= to keep track of my expenses.

Los gastos would be more general: the expenses (maybe of a project, a family, a company, etc.), and you’d normally need context to know whose they are.

Here, you’re talking about your personal account and your own money, so mis gastos is the natural choice.

Do I need the preposition a before mis gastos, like controlar a mis gastos?

No. You don’t use a here.

Spanish uses the personal a when the direct object is a specific person (or sometimes a pet):

Veo a mi hermana.
Ayudo a mi amigo.

But gastos (expenses) are things, not people, so no a:

controlar mis gastos (correct)
controlar a mis gastos (incorrect)

Why is the verb in the simple present miro and not estoy mirando if it’s something I do regularly?

In Spanish, the simple present is the normal tense for habits and routines:

Miro el saldo cada semana. = I (usually) check the balance every week.
Voy al gimnasio tres veces por semana.

The present progressive (estoy mirando) is usually for actions happening right now:

Estoy mirando el saldo ahora mismo. – I’m checking the balance right now.

English uses “I check” / “I’m checking” differently from Spanish, but for regular habits, Spanish prefers the simple present: miro.

Could I replace miro with reviso or consulto here? Would that sound more natural?

Yes, both are possible and common, with slightly different nuances:

Reviso el saldo de mi cuenta…
– revisar = to check, go over, review (often to see if everything is correct)
Consulto el saldo de mi cuenta…
– consultar = to consult, check (often in more “official” or formal contexts)

Mirar el saldo is very natural and everyday in Spain, especially for quickly checking your balance on your phone or online banking.
Revisar and consultar sound a bit more formal or careful, but all three verbs work.