You will need HKD (Hong Kong Dollars) to transact when in Hong Kong. Apart from bitcoins and other digital currencies, you will need HKD in Hong Kong.
Yes, digital currencies are regulated in Hong Kong by the Securities and Exchange Commission.
Some of the payment methods that are readily accepted in Hong Kong include American Express, MasterCard, and Visa.
You can buy bitcoin in Hong Kong via automated teller machines or through any Hong Kong trading currency exchange like Coinmama or Kraken.