In the Standard version of Question Writer 4 these options (apart from Override Body Text Font Color) can be found under Quiz Properties - Appearance Settings
By ticking the box and selecting a font you can override the default font used in the theme, for example if you want to customize the appearance of the quiz
You can override the default font size used in the body text. This might be useful eg if you have particularly long questions and have trouble fitting them on to a single page.