@lettereye
I am author of the woothemes paypal advanced payments plugin. Yes it is not possible to place the form in the checkout page because you need to pass the order information to get the securetoken and using securetoken we can build an url for the IFRAAME, which inturn get the payment form from the PayPal site.
It is better to have SSL for your site to avoid “mixed content” warnings. You can refer to the documentation at
https://wcdocs.woothemes.com/user-guide/extensions/paypal-payments-advanced/