I'm having a hard time finding a RichTextBox or equivalent in GTK.  I've found TextView, but not any info on how to create one.  Anyone got any info?

You need to use it in conjunction with a GtkTextBuffer.  If you haven't already, check out <prefix>/share/gtk-doc/html/gtk.  It's an excellent reference for GTK functions, though it can be a tad short on examples.  Also, run gtk-demo to see various widgets in action and find out how they're named in GTK.