If you want have many clients you must use CRM-system.. Our company started using CRM-system BPM'online https://www.bpmonline.com/. It is really friendly and easy system. The contacts can esily imported to the system from excel, It is modern and pleasent to work with, while the system gives the most progressive standard for the process modeling. You can discuss with your colleague or agreements, all work will be saved. You can to control the finances and monitor customers!