On point 1 - if you do have your blog already stuck on a subdomain (blog.site.com) this a neat solution to serve it through site.com/blog that might work for you: http://www.seomoz.org/blog/what-is-a-reverse-proxy-and-how-c...
These issues were fixed by doing slightly more complicated proxying rules and by filtering the cookies as part of the proxying.
Reverse proxying is a really powerful technique (you could sit things like mod_security in front of your relatively vulnerable WordPress install, for example), but unless you have an experienced sysadmin on hand to help if it all goes wrong it's probably not something you want to try based solely on an infographic.