Sorry for the delay in replying.
1- Currently TemplateToaster doesn't support fonts in EM, but it is in our to do list.
2- CSS3 font-face property is in our wish list, it'll be available in future versions.
3- Sorry for the inconvenience, please visit following thread:
http://templatetoaster.com/forum/viewtopic.php?f=5&t=5504- I'll advise you to use only web safe fonts from local machine's installed fonts.
5- Currently a separate font size configuration option is not available for responsive design.
6- Thanks for the "stylizer " suggestion, we'll consider it in future. Did you notice our custom CSS option which is under: File-> Preferences