Have current joomla sites. Want to enhance existing custom developed document request functionality to an environment where multiple clients can us it.

Current functionality: Document Requestor creates profiles, logs in, uses custom forms to order documents, enters credit card info, and submits data. Submitted data goes through a workflow including document logic checks (i.e. card info is valid number digits, etc) sends emails to client and client admin informing of new order. Admin signs into secure page to get order and manually process credit card. When order ready, admin changes staus which notifies client via email that order ready

Desired functionality. Same as above, with following enhancements: Ability to have a multi-tenant system so that support multiple clients, and client admin cannot see orders of another client. Ability to modify admin and systems emails, and pricing on a client by client basis. More info to chosen developer.

Prefer to use as many Joomla extension as possible in order to speed development. MUST be very familair with Joomla.