Hi We are working on a project and have decided to go with the multitenant Saas architecture level 4 and the Shared database shared schema approach as shown on this page http://
Take a look at TechCello. it covers not only the multi-tenant architecture but also maintenance for billing, etc.
• Create Subscription
• On-Board Customers
• Configure Customer
• Setup Customer Security
• Setup Users
• Permit User Access
• Monitor and Control
• Bill/Track Payments
• Renew and Upgrade
I am not affiliated with them. I just happen to be looking for the same thing.