Design Accounting Module for the ERP Software

Hello, We are building a ERP software for small and medium scale businesses. We would like to design an accounting module in it (something similar to zoho books, quickbooks and open source - [login to view URL]). We are already in progress to design/develop modules such as HR, Payroll, Project Management, CRM, Sales, Purchase Order - Sales Order. Design needs to be extremely intuitive - and self explanatory. Maximum information will be helpful but it needs to be to the point. Solution architect should also need to add screen mockups. It needs to cover at least below basic functions, however - we want your expertise to design an entire to end to end functional document covering many other recommended possible features (with explanation - sky is limit): Chart of accounts Sales Invoice, Purchase Invoice, Journal Entry, Customer Database, Supplier Database, Bank / Payment reconciliation, Period Update/close/open ? Payment tools, Reporting functionality etc Payment gateway? Accounting needs to be able to support everything under ERP: Estimates: Send new proposals and get them approved from customer. Price List: Customize price lists for the customers, for the items you sell. Sales Orders: Confirm customer’s order and ship goods soon. Purchase Orders: Create and send orders to purchase goods. Retainer Invoices: Collect advance payments or retainers from the customers. Timesheet: Track time for projects and bill them to your customers. Thanks.