I want to develop themes for wordpress packaging, but I did not want to start from 0, can I buy a theme with extended license, create my theme using it as a base and sell?
If you mean sell here then no - not with either license.
If you mean outside envato then every project, website, use would require an individual regular or extended license depending on the functionality of that site.
Neither license allows use on more than one website or domain
No, but there are a lot of free and paid starter themes
Roots / Sage
This one requires a high knowledge of PHP (OOP and MVC, it’s not the classic way of copy-pasting code, which is usually found in WordPress)
There’s also Underscores but I would not really consider it.
You can check github for more starter themes or themes licensed under MIT.