if the business already existed, and is now just switching to double entry, its assets, liabilities, and owners equity would remain the same, as this is required for the accounting equation to balance. the owner would have bought any previous assets and they would already be included in the capital.
if the business didn't exist before, how can it have assets without the owner buying them.
i'm confused, can you provide the specific question for this?
also, addressing your concern of recording opening balances, they usually give you everything except the capital, which you have to work out by recording all the assets and liabilities first then balancing the debit and credit sides.