1. No, you do not have to register the domain to have hosting for that domain. You just need to go to our website and enter in the domain you want to be hosted. You can do so here:
http://www.dynadot.com/web_hosting/about.html
2. Yes, when you log into your Dynadot account, you can check the bandwidth and disk usage for each of your domains.
If you have any other questions, please let us know.