All of our products on Envato are using Split license, not GPL license; so, each regular license can be used for only one site. You will need to purchase more license to use for more sites.
Our support covers getting setup with the theme, theme related questions and bugs or issues that occur when using the theme. Customization can be any work you need done to the theme that is not covered by the scope of our support. In most cases, this is anything that falls outside of the options the theme offers. While we take custom projects occasionally most of the time we are busy working on new themes.
However, the good news is that you will find plenty of quality developers and designers in the new Envato’s website – Envato Studio.