Exact pixel sizes are not a good way to go - they are not responsive to different screen sizes and resolutions.
Yes, but you do need to pick a default font starting point to design around that sets the tone for the overall look and feel of the page. Obviously the font can be scaled up and down based on the media after that, but you must start somewhere!
light grey fonts.
People forget the over 40 crowd may not always have an issue with the size of the font but the contrast of the font and the background can be a real issue. Light fonts on a light background or dark fonts on a dark background color that reduces the reading contrast is a tab closer!
Besides, we already know that Google has been evaluating CSS to see if people are cloaking text, such as white font on white background, for keyword stuffing purposes so evaluating the text size is probably another signal as well.
I think overall font size and text density may be used by Google as one of their bazillion signals of site quality that could tilt their opinion of whether your site is quality vs. spammy. For instance, putting 100 words in an <h1> tag or a really big font might be considered a tad spammy. Likewise, putting a lot of text in a font size smaller than 10pt would also probably set off some potential keyword stuffing bells and alarms.
In other words, if the page doesn't look 'normal', the algo probably flags it, bags it and tags it as "not intended for humans", so care should be taken with picking fonts IMO.
