I'm away from my PC for a little while, so I was wondering, does SD4 support the html5 semantic elements such as footer, article, header, etc.? If not, would I uses the HTML Element option to add or edit them. Otherwise I would have to add them after exporting right?

Yep it sure does,
in the "Content" tab where you choose the type of container from the dropown menu
In the
"Elements' tab, where you can change the "Div tab, to whatever you want from the dropdown menu
or
in the "Structure Data" tab
The "Structure Data" tab allows you to choose the Schema type if you want to go that into structured data

Thanks, I'm so bored at the moment that I'm reading html specs! I'm still trying to learn sd4 and did not recall if that was an option.