There is no co-pay with O class. When you check into your flight you'll be able to see in the app the Standby and Upgrade list and it will show you your position on the list. Note that your position can and will change as people with higher status check in.

You will not have to pay any fare difference. The eUps are the currency.

Note that the rules of your purchased ticket will still apply so you will get 125% mileage, not 150%.