Thanks for your answers!

That is a option to achieve my goal, but it has a major disadvantage - at least when I played with it:

Limiting formatting to a selection of styles disables also the regular formatting options; i.e. no changes of the font, font color etc. will be allowed.

If I choose that approach people will hate the template and not use it.

Do you know if there is a way to restrict formatting to a number of styles but still allow for the regular formatting options?