How limited am I when working in WordPress? In terms of front end customization (JS, CSS, HTML) and “back-end” customization (implement a new feature on the site, as said about the “tutorial shop” section)
You’re only as limited with your knowledge of WordPress and programming. You can make changes to the frontend or backend by using or creating your own plugin(s). The same goes for creating your own theme or using a child theme to further modify an existing theme.
Can I achieve that goals easily with WordPress features? I don’t know which tools I actually depend to achieve that.
With some research on setting up WordPress as an ecommerce, yes. There are plenty of plugins and tutorials to turn WordPress into an online shop. Just a matter of choosing the one that’s right for you.