The main purpose of the font settings is to allow you to change the font size. Currently, the options allow you to pick any size and any font. This could lead to someone making mistakes, since they might select a font that isn't readable, or they could pick a size that is too big or too small.

A better approach would be to predefine three or four font sizes and allow the user to pick from them. This will simplify the preferences and reduce the amount of work for the user. It will also help to prevent mistakes.

Mockups: https://raw.githubusercontent.com/gnome-design-team/gnome-mockups/master/notes/prefs-import-location-wireframes.png

The only relevant part is the app menu.