pre-sales questions

Forgive me if this is not the correct forum, please direct me to the right contact/area. I have been using webmin/virtualmin GPL. I am considering upgrading to the paid, but would like to ask some questions. I have seen the list of basic features that you have on your site, so I know the fundamental differences. But it took me a while to get the GPL version the way I like it and I would hate to have to start over with different caveats on the paid version. Here are some of my questions (in no order of importance):

• Is there better integration with nginx?
• is there better integration with PHP-FPM & OPCACHE?
• Is the licensing per server?
• Is there an easy way to fall back to GPL after a PRO upgrade?
• Is there a full list of supported Linux OS's with versions?