Marketpress currency questions

Hello, we'd like to ensure that all prices on our site are in USD.

I see that the marketpress-data.php file in the marketpress-includes folder has a big list of currencies in it - starting "//currency list - http://www.xe.com/symbols.php
//last perameter is symbol which is unicode hex: http://www.mikezilla.com/exp0012.html
$this->currencies = array(
"ALL"=> array("Albania, Leke", "4c, 65, 6b"),
"AFN"=> array("Afghanistan, Afghanis", "60b"),
"ARS"=> array("Argentina, Pesos", "24"),
"AWG"=> array("Aruba, Guilders (also called Florins)",

and so on.

Would I be right in thinking that if I delete everything in this list except for USD then the drop down menus in the store settings will have USD as the only option? Is this a safe thing to do that will not have worrying consequences?

Also, please could somebody tell us whether a seller can choose USD for their paypal currency even if their paypal account is NOT set up with paypal to have USD as their primary currency?

Thank you.