You can make any field (or any widget, for that matter) invisible by selecting it with the Widgets tool and choosing "Widgets -> Show None" from the menu. It's also possible to position widgets outside the visible boundaries of the card, but doing so would make them a real pain to select and edit.
Buttons can only contain plain text, in a single font. You can change the font of a button (or the default font of any widget, for that matter) by selecting it with the Widgets tool and choosing "Widgets -> Font..." from the menu. If you want icons or more complicated rich text "in" a button, you can set it to "Show Transparent" and draw on the card background underneath it, or position other widgets beneath it.
Does that help?