You are purchasing a lifetime licence, which you will receive immediately after payment.
If you ever move your Commentics installation to another domain, just log in to your Client Area and deactivate your licence. This will allow you to activate it on another site.
As the licence provides unreturnable items (modules, developer time), refunds are only possible in particular circumstances.
Support is provided via the Forum and is community based meaning a developer response is not guaranteed.
Support is provided via the Client Area, is private and has a guaranteed response within 48 hours (often sooner). Each response is worth 5 credits.
To see which modules, languages and themes are available, see the Client Area informational page. More are regularly added.