What happens when I open a payment channel on the live network?
Where does the destination account come from?

The uplink that you use (in this case https://github.com/interledgerjs/moneyd-uplink-xrp), has a list of upstream connectors (https://github.com/interledgerjs/moneyd-uplink-xrp/blob/master/connector_list.json). With the --advanced flag you can set the parent connector to anyone you want; the connector list just provides some defaults.
When you start moneyd, it opens a websocket to the connector. Some messages are exchanged to trade XRP account details, and two payment channels are opened (one from moneyd to connector, one from connector to moneyd). After that point, the websocket connection is used to exchange ILP packets and payment channel claims.
why we have very few parent connectors to choose ? Should codius itself run some connectors to make sure it is always available.