Hi,
However, I get a box for Credit Card details in the checkout, but can't add address fields or an email field. It seems that this is required, as PayPal only collects information for their users - I want to use them to process credit cards and nothing else.
I am sorry but I don't understand what you're trying to perform.
The Paypal pro plugin just ask for the name and the credit card information ; nothing more.
And more than that, because the user is logged, you already have his account and his addresses (billing and shipping) so you do not need to ask him ; you already have it (except if you removed the "address" and the "login" step in your checkout workflow).
Regards,