asp.net - Windows Workflow Foundation: Recommendations how to design architecture -

We are running many similar ASP.NET applications (one per customer) on the basis of our custom frameworks. Each application uses its own database (initial catalog in the connection string period). Now we want to add workflow capability (exactly 4.0;) to applications so specific workflow will be the same for all applications, only some initial settings of each workflow can vary, e.g. In an application the e-mail will be sent to User X, but for other users, the Wi

I have several common questions about how to design architecture:

(1) What could be the shared workflow database for all applications?

(2) To host a workflow engine - Inside our custom Windows NT service or inside the IIS? What are the criteria to choose the right host?

(3) How should the workflow engine communicate with the application? Should some WCF Endpoint API be configured in the application workflow host or voice poem - will each application provide the WCF Endpoint API and the workflow engine will call it? How will the workflow engine identify the applications? In both cases maybe some application identifier is required as a parameter in the API call?

(4) We also want to store some information in the application database on the basis of workflow states. Is this possible?

Thanks for the suggestions!

I will follow Robert's suggestion and write different questions, this is the first