Realise this is a proof of concept but would refer to Themes with Visual Editors and in effect customisers without code that already are quite sophisticated in Theme frameworks aka HeadwayThemes and others. It provides for extensive typographic controls is very user friendly etc.

To do all of that within the confines of the 'Customizer' seems a shame not to learn from existing editors that already do this quite ably in existing solutions. I do of course defer to Justin's superior knowledge on these matters. But just a thought.