If you are thinking on buying a license for the Avada theme, the best thing is to buy it directly from ThemeForest
Acording to Theme Fusion (Parent Company of the Avada Theme)
When purchasing Avada (or any WordPress theme) via the Themeforest marketplace, you have two licensing options; The Regular License, and the Extended License. The regular license will suffice for 99% of users. The purchasing process, invoicing and licensing is facilitated by Envato
Also, when you purchase Avada, your Avada WordPress theme purchase includes several bundled plugins; Fusion Builder, Slider Revolution, Layer Slider, Advanced Custom Fields PRO, Fusion White Label Branding, and Convert Plus, and do not require additional licensing in order to use with Avada.
That is from the author itself, you can read more about it here
You need to use token key. According to the author:
As of Avada version 5.0 the 3-step Product Registration process has been replaced with a new Token Registration method. This change was precipitated due to Envato soon deprecating their old API in favor of new and improved API management. This new setup allows for a faster, more reliable and secure setup. Token Registration will be required to receive automatic updates, Avada demos and premium plugins (to install and update the Revolution and Layer Sliders).
Can you use your license for several Avada websites?
Well that is a big debate. Obviously if you ask Envato and the authors the answer is yes. To be honest, if you ask me, the answer should be yes too. But (there is always a but…) I do believe the price for extra licenses should be different than the price for your first license.
Here are some excerpts from an interesting discussion on the topic
You need to purchase a license for each time you install a theme on a unique website.
Great question. The policy of envato says that you must use one licence for one particular website/URL but what if when i use same theme for another Websites??? How themeforest as well as author know the sell item are belongs to this this urls ?? There is no any facilities provided by envato to secure that theme for one website
as @OsamaSayegh says you must buy another licence for another websites ?? if buyer easily use same theme for another url then why he/she can purchase another?? for now there is only hardly 2-3% author provides licence validation theme which require licence key before use but it still not secured. Any one can break those code easily with few of developing knowledge.
So finally for buyer you must buy another licence for your new website if you want support from those theme owner.
Each website = buy 1 copy of the theme (that’s the license)