Ciao Giovanni.

Not necessarily, it depends on what you want to achieve for the end result, how these sites are supposed to differ from each other. If only the content displayed in the component area, then no.

Hi Paul, I would like to have: 1 home page with some Joomshaper Addons 1 page template for articles and portfolio 1 page template for some product

If header, bottom and footer area should be the same on all pages, you have to work only with component(s) and modules, and keep the same Template Style. The same as you worked in the past with different template.