I feel that the typeface used in the Ask Question textarea does not look good, and that the font size there is too small. How can I change them? Can they be changed network-wide by SE?
There is no way to change the fonts, font size, etc. which is embedded in the editor.
To correct the size issue more quickly (It's currently a standard 12-point monospace font) hit CTRL-0 to zoom to the default level (in case you've zoomed out). If that's not sufficient, as Robert Harvey suggested in the comments, zoom in with CTRL-Mouse wheel up (or CTRL-+).