You are able to add as many users on to the system as you would like to. This will allow you to start effectively managing your account and ensuring all customer information is logged and any notes made are all stored within one system as well as any leads and sales, emails or sms that may have been sent and any letters that have been written. Not only will this give you a clear representation of the interactions with your customers but it will allow you to run reports and assign tasks to them.
Here are some relevant documents:
How many users can I have on the system?
How can I stop users accessing certain modules within the system which I wouldn't like them to see?