i believe the $500/month ceiling can be lifted by adding a credit card or social security number to the account (i forget if either will work or just one or the other... or if both are needed). whatever email address it was setup under is where the customer needs to pay. there is a handy feature on the menus called request money, and with that you can send the customer a money request or invoice to her email address.
be aware that with a premiere or business account you will have fees taken out of any payments, even if they pay from a bank account or money sitting in their paypal account (though you would with a merchant account to take credit cards directly as well). no fees for a personal account, but you cannot accept credit cards through a personal account and it is also against paypal's policies to use a personal account for business (they will fine you if they discover you have been).
i believe all of this information is spelled out in their policies and can probably be found searching in their help section. it's a bunch to figure out at first but once it is setup and you have a little experience with it, it's pretty easy to get paid, transfer money, pay someone, etc.
hope that helps a little!