The Professional license is priced per internal employee, with a minimum of 10.  You may host as many companies as you want, each with as many users as you want.  You may charge anything you want to your customers.  There are no additional fees or licenses to us.  We call this our free hosting license.

We recommend that you create a separate SQL Server database per customer, but maintain a single ASP.NET application for all your customers.  That is, unless you do some custom work that only applies to a specific customer.  SplendidCRM can be configured to pull its database connection string from the Registry or from an alternate database so that a single site can support multiple customers.  We use the Registry technique on our eval site http://eval.splendidcrm.com.  We can even provide you with the code to our eval site so that you can see how we dynamically setup a new SplendidCRM site.