I have an HMTL website that I'm converting to WordPress so it can be managed easier. There are probably about 30-40 pages on it right now. It's quite messy. All of the URLs will be changing, and lots of new content and images will be added. How do Google rankings perform when most of the current indexed URLs change to 404 not found? Oh, and this is a business's website, not a Adsense or product site.