What are dos and don'ts while creating a theme for prestashp 8.1 to be upgradeable to newer versions in the future?

[John Zaw]

what I am currently doing to create a theme is

-  copy classic  theme, edit theme.yml file. Now I can select new them from back office.

but the theme I want to create is completely different form classic theme. So, I decided to create a new theme from scratch and I have several questions while trying to create new theme.

- which files should not be edited to be upgradeable to newer versions in the future?

- I have knowledge in these languages -> Html, sass, laravel(I don't know symphony framework), js, smarty. Can I create a new theme with current knowledge or do I need to learn more?

- Is there any available online resources(books or websites) that describe us more details about creating themes than it's own documentation?

Thanks in advance for all answers. Have a nice day, developers!