Centralized database with billing

We would like to create a centralised database, where the information from the 12 Websites which we manage will be collected. There will be a centralised data base with customer information which would eliminated doubbles when clients sign up with serveral website of ours. The database would manage the payment process, each website having a different payment system and there would be one centralised billing, which would be easier for us to manage. We would have to create gateways to cube 3,1 websites, Joomia and normal websites. The centralized billing would comunicate with the bank for credit card payments. This has to be an easy to use database, where a normal accountant can see immediately what has not been paid. We would also have to be able to seperate the different databases from the different websites.