I can start looking into it, starting with a normal system font.
In terms of exporting a field using bitmap font, I expect it being not that different from the properties of a normal textfield object, except it would point to a bitmap font definition, which is similar to a tileset but with optional kerning properties per character. Most bitmap fonts in editors/engines assume monospace, so kerning could come later.
For instance a bitmap font def would have a source image, tile width/height, margin, spacing, and a list of characters in the image from topleft to bottom right
and the textfield object might just list numbers_small in the font drop down, or there's a radio button to select bitmap font over system font which affects the dropdown contents