1. Would you have the blog on a subfolder (blog.xenforo.com) or subdirectory (xenforo.com/blog)? It will obviously be about the same stuff as the main site/forum.
2. Would you have a Wordpress-blog as your mainsite and the forum as a subfolder/subdirectory, or vice versa? Would you lose a lot of potential members for not having the forum as a main site?