Admin,
I think the font size is good, It has variation with the topic at 14 pt, the message smaller and signature even smaller.
as for the layout of the messages, I would suggest that the date of post be moved to the top line, and add back the title of post as it is now, then message and then signature. then a line for end of post. everything in a compact, contained area.
Seems to me there is plenty of space winthin the messags space that a reply button could be inserted there. I can't find a reply button at all.