Hello,
1.You can hire a developer to create the payment gateway you need.You can choose one of our
certified/community partners.
2.At the moment the default payment gateway is PayPal and the currencies available are the currencies PayPal supports.
3.After the listing expires it remains in the user's dashboard where he has the option to re list it.
4.Yes it is and child themes are the recommended method.There is a list of of
certified/community partners you can hire for this.
Please let me know if you need more information about the theme.