Tabs and Accordion Section

Those are definitely better off in plugins as they would use shortcodes.

Shortcodes should never be inside a theme, as if you change themes, you'll be left with empty shortcodes all through your content.

There's a lot of cool free plugins available out there that allow you to create horizontal tabs and accordions :)

thx. Wich plugins would you suggest?

This is a cool one: https://wordpress.org/plugins/jquery-collapse-o-matic/