Looking good, Dave. Evolution rather than revolution.
1 – “I am also thinking a width of 520 pixels seems a little cramped for 16-pixel type.” Agreed. Your page is constrained to 940px at the moment and I’m sure that could stretch to 960px with no complications. Opinions differ, but try a search on “web page width 960” and you’ll see it’s quite common.
2 – your comments about being a one-man blog network mystified me. What is he talking about, I wondered? After a minute or two, I finally noticed the grey nav bar with the four sites, at the top. To my eyes, it merges completely with the grey tabs in my browser (Firefox/Windows). Not an issue in IE or Chrome, but you might want to consider making it a different colour so it stands out better. Same colour as the sidebar background?
3 – I’m not particularly keen on the two-column sidebar, it looks rather busy. I might like it better if it wasn’t boxed and with a background colour, or if the main content was slightly wider. At the moment I feel it’s rather inappropriately dominant… it feels like it’s pushing the main content to one side.
Hope this is useful.