Backend for coaching website

I run a coaching consultancy with a team of teachers and clients who book one-to-one training sessions. I need a backend to my website that will accomplish the following: A database to keep track of client enquiries and a booking system to track history of clients booking sessions. Clients booking sessions with us are given a log-in to the following booking system which contains; A passworded page for my clients to log-in to which will allow them to make payments online, track appointments made and how many they have left, recommend friends and receive a free credit, see contact details of their coach and click through to email them, change personal details including password. Password reset has an automatic email confirmation. There is an automatic password reminder email if they forget their log-in. A passworded page for my teachers which will allow them to see which clients they have and their contact details, how many sessions they have paid for and have left, to input dates of sessions taken by their clients, and to see the whole client history. The ability to send out a standard email payment reminder if their clients fall behind. A passworded admin page which allows me and my admin staff to view all current clients, their tutors, sessions paid/taken. With the teachers it should automatically list all sessions taken with the rate teachers are paid (this varies). This should automatically generate an invoice for those teachers. We need to able to access a database of all past clients and their history with us. Admin page should also be able to add dates of sessions taken to the system and alter all this information in case of need to make refunds. We also need to be able to use the database to send out newsletter/promotional emails to different groupings of clients. Admin page should be able to see password of all clients and teachers. I can show you some example pages from personal training and pilates sites. Basic design should fit in with our website. I currently want this to work with Google Checkout and/or Paypal. I already have a Google Checkout account and will set up a Paypal one specifically.