Thanks for the follow-up.At the end, I like to be able to use PayPalPro (including forms and coupons) on a WP Multisite for each website in the installation.
What you've described is certainly possible with s2Member Pro Forms for PayPal Pro. You can certainly use s2Member Pro Forms on each of these sites, and in combination with Custom Return URLs on Success, you can redirect a Customer to any page you choose after checkout is completely successfully.
Regarding the ability to sell Blogs too...
This is also possible, but in this case you would need to activate s2Member on the Main Site of a Multisite Network installation. All sales would be processed on your Main Site, and access to create a Child Blog on your Network can be granted after checkout is completed, via
/wp-signup.php. You might place a link to this Blog Creation form on your Login Welcome Page of the Main Site.
For further details, please see this section of your Dashboard, on a Multisite Network installation of WordPress. See:
s2Member -> Multisite (Config).