Create a web app that allows appointment bookings specific to each customers contract

I'm currently using two different websites and filemaker to scarcely do what I envision for my Recording Studio. I know a bit of code, but this is beyond me and I am too tied up in recording and writing music. I am looking for a simple and elegant process that allows my customers (bands / artists) to book sessions on my website, pay deposits etc. I currently create a secure webpage for each band where they can log in and see their latest projects (songs). - At the moment I have to create this manually in squarespace, then email the band the password. Ideally a create account button would be best, but only when the band has signed a recording agreement. Here's the really hard part (for me at least). Using Agendize, I have iFramed a booking process into each personal band webpage. This allows the band to book sessions (subject to my availability), pay a desposits etc. However, Each band pays different costs.. again this is when a personal login comes in handy, which is something I cannot seem to make. I have made a quick process map to hopefully explain the process better. On the back end of it all, I need booking data and financials from my customers to come together to show on spreadsheets for standard business purposes. In the end, it will create one awesome way to book sessions at the studio, and will hopefully be a huge success. Sadly, I don't have that kind of skill to make it myself. The studio so far has been a real success and I am about to launch a new recording space. I have a vision and so far I have great support and feedback thats tells me I need to keep pushing. I really hope someone can help, and can see the benefits of what I am trying to do. Thank you.