Regarding the white space issue - I don't think it is the actual white space that is the problem - the problem is the contrast between the white background of the text boxes and posts against the beige background of the page.I think simply getting rid of the beige and making that white would make a world of difference.
As for the fonts, I think the problem may really be mixing too many similar styles. Even though they may all be set in say 12pt, how 12 pt looks in one font looks very different than in another. Pick just one or two fonts altogether and you will probably increase readability by a substantial amount as well.