Very sticky question there Mr. PSTester. As Darrel has stated 10,000 might be enough, but then 1 per font type would be the minimum, even though you would be a poor tester if that's all you tested. Don't forget some clients have different sets of fonts, those using Linux, or another OS may have completely different fonts. Are you also planning on testing all the font sizes too?
Success is the ability to go from one failure to another with no loss of enthusiasm.
~ Winston Churchill ~