A custom domain can include more than just one blog, though. You can setup multiple blogs in one domain, limited only to your imagination, and the virtual hosts limitation of your domain registrar.
Here, for instance, is how I setup my custom domain, "Nitecruzr Dot Net".
- I setup a home blog for the domain, which will index all of the existing blogs. This was a new blog, "nitecruzr-dot-net.blogspot.com", which I published to "www.nitecruzr.net", using the "Buy A Domain" wizard for the new domain "nitecruzr.net".
- I defined additional virtual hosts in "nitecruzr.net". Each additional host, just as you may have setup the "www" alias, is another pair of "CNAME" referrals to "ghs.google.com" - added using the DNS management wizard provided by your DNS host or domain registrar. If you setup your custom domain using the "Buy A Domain" wizard, you use the eNom or GoDaddy DNS Management wizard.
- I published my existing blogs to the newly defined virtual hosts. Each blog is simply republished to the custom domain, using the "Advanced Settings" wizard.
You can do likewise with your blogs. The only limit here, IMHO, is your imagination.