Barry,
There are three primary ways to get CRM licensing. You or your customers can get CRM Online, which I believe that you will get a referral fee for. With CRM Online, you won't have any cost of maintaining your infrastructure because Microsoft is providing the entire service for you. With CRM Online, there is no external connector license.
If you are setting up a business to provide the application to multiple clients, you can also consider partner hosting (SPLA). This licensing model allows partners to host CRM for clients and pay Microsoft per user per month. As with CRM Online, there is no requirement to purchase an externl connector.
Finally, your clients can purchase their own on-prem license of CRM. If your solution has a self-service customer portal, you will also require them to purchase an external connector license.
As Julie mentioned, you only have to pay for CRM licenses for the 'users' that require access to the CRM user interfaces. If you build a web portal that surfaces some of the CRM functionality (such as helpdesk), you don't have to count external contacts as user licenses. In laymans terms, if you build an XRM application with contacts for your external customers instead of using users, you won't have to pay for user licenses. The design of each XRM application is different, but for the most part, what Julie says, considering the people inside the company to be users and outside of the company to be contacts is good guidance.
Good luck!
Shan McArthur
www.shanmcarthur.net