I'm going to be buying a large hosting package with unlimited addon domains, mysql databases, etc. if I want to run multiple sites off this, how would I begin?
Buy the hosting with those features ex. hostmonster. Buy the domains that you want to host on the hosting account. In the host's Cpanel add the domains. In your domain registration account ex. godaddy, set each domain's nameserevers to your hosts. If you have any specific questions let us know.
if your hosting package will have cpanel, get the package with web host manager and you can add on many domains with their own seperate accounts. I believe its called a reseller account.