Learn Spanish (Latin America): Si hubiera comprado esas casas, tendría mucha riqueza. - If I had bought those houses, I would have a lot of wealth.

This is a mixed conditional. It describes a past condition that didn't happen (using hubiera comprado) and imagines what the result would be right now in the present (using tendría). Because the condition is in the past but the result is in the present, the tenses are mixed compared to a standard past-to-past scenario.

Could I say hubiese comprado instead of hubiera comprado here?

Yes. The past perfect subjunctive has two valid forms for the helper verb: hubiera and hubiese. They mean exactly the same thing, though hubiera is much more common in everyday Latin American Spanish.

Both hubiera and tendría share the exact same forms for yo, él, ella, and usted. How do we know this means 'If I had bought'?

Without surrounding context, it could just as easily mean 'If he had bought' or 'If you had bought'. In real conversations, the context makes the subject obvious. If there is any ambiguity, you would simply add the pronoun, like Si yo hubiera comprado.

Why use mucha riqueza here instead of just saying mucho dinero?

While mucho dinero (a lot of money) works fine, mucha riqueza specifically translates to 'a lot of wealth'. It implies building a long-term fortune or having valuable assets like real estate, rather than just having cash on hand.