Font size is a bit trickier. A general design rule concerning fonts is to sparingly use big font sizes, and especially, never use them for body text. Remember that a font smaller than usual may look professional and information-dense, while the same text set in a size above the average may very well be regarded as something too irritably amateurish. Fortunately, the FACE attribute has a means to account for this. Browser scans the font face specification left to right and enables the first face encountered that's available on that system.
Font names are case insensitive.
Sans serif availability is a great relief to Web designers. Surely, such a basic font type is what they've been starving for so long. Of course, you can specify any font name in the above declaration, but it makes little sense unless you don't mind that only a little share of your users will see the improvement. Another issue to beware of is that, even if you set the same font SIZE for different font families, don't expect them to really look the same size. The same holds for nonstandard fonts as well.