Unfortunately SF blogs don't support any fancy text options like size or color.   If you enable rich-text you can set the font family as well as bold  and italics but unfortunately not size.

I do not know.
If you need a bigger font, you may need to change the settings on your own computer as my reading of text is not inhibited by the size of letters.
The difficulty in reading some blogs has mostly been focused on lack of theme, content, grammar. Focus on those things and I do not think font size will be an issue.
-pip

All I want to know is how to increase the font-size for My blog -- so that you, Dear Reader, can benefit from My wisdom....

I've nothing against the little furry chaps Myself, you understand...

Well?