Hi folks, going to Hong Kong for the first time soon. Asking for advice about payment methods, must-download apps, etc.

1. what's the best payment method in HK? Is a US credit card works well in most merchants/transportation? Or HK Dollar is better? I heard `octopus card` is mostly accepted in HK. Where to get the card and can I fund the card by depositing US cash?
2. is there Uber-similar apps for a taxi in HK? What are some useful apps which are good to have before visiting?

Thanks!