Hi there,
A Small Business License allows 10 such names
An IP license enables all the domains/subdomains hosted on this IP@ to use the control.
All license options are good for http://localhost. I'd highly recommend Small Business License as it's the most popular choice among our customers. Out of the 10 names, you can use one or two for the internal dev server ie. http://intranet while keep the rest for your production servers. With Small Business License, you can start with a couple of names then add on more later. There is no deadline when to submit the last one. SMB license only locks to the alphabet domain/subdomain name registered regardless of IP@ underneath which means switching ISP or moving server while maintaining the same domain doesn't require license file update.
IP license is good for unlimited number of sites hosted on 1 IP@. If you have many sites sharing 1 IP then IP license is the most cost effective choice. The disadvantage of IP license is the IP@ change fee. You have up to 6 months to submit the production IP to make your official license file. In the meanwhile, you will be given a full functional temp license to cover the transitional period. This temp license is good for any IP@ until expires therefore you can test it on all servers in questions and eventually settle down on a production IP. Once an IP@ gets registered, change of IP involves a fee.