1. I saw an article describing how to do this (
here), but it does not rewrite existing URLs. I have created my own modification which redirects old "member.php"-style URLs to the new username type URL and it works well, I may release it here.
2. It depends on your needs - have a look at the vBBlogs out there, and then maybe install Zoints Local on your own test board, and have a look which one you think suits you better.