I don't think there's a one-click super easy way to edit font/size etc with the docx module (yet, at least). Fortunately, it's relatively easy with lxml and it's not too difficult to get a basic grasp of the xml format with a bit of poking and prodding.
Try changing the extension of your file from .docx to .zip, and open /word/document.xml. The elements there that modify specific text are children of both the w:pPr (paragraph properties) and the w:rPr (run properties) elements. This link provides a good overview of the methods that you can use to sift through the document.xml file and add/remove/edit as you see fit.
I'd also suggest looking at the "def paragraph" function in the docx.py module. There are a couple of direct examples there of appending various descriptive elements to paragraphs and runs in there.