I've run the checkout wizard again and the paypal payments seem to now be going through OK (although it redirects back to an https connection for the pp_confirm.php page, which of course doesn't exist yet because I'm still waiting for client verification for the SSL). If I change it to http the page loads, I get the confirmation email and the transaction goes through.
I still can't get the card details div to show on the checkout page though - using Inspector, I can see that the payment wrapper div is as follows:
div id="payment_wrapper" style="transition: height 1s; overflow: hidden; height: 0px;"
Selecting payment by Visa/Mastercard should presumably display this div, but it doesn't - how can I fix this?