Best Invoice, Payment and Accounting Integration Combination

Looking for suggestions for best-of-breed solutions (reliable, well designed, and reasonably priced) to generate invoices, accept online payment and integrate with third party accounting system.

This is the target functionality:

1. Import/Export (at least one way) product and service description and rates between accounting sytem and Sugar.

2. Generate invoices from within Sugar by picking Account, (preferably also associate with a Case but not required), and Contact to invoice, add product/service line items.

3. Email invoice to contact and include payment button/link on invoice to allow customer to make online payment

4. Optionally if customer provides payment information by phone, staff issues payment on selected invoice (I would guess this would happen through a virtual terminal on payment processor website instead of within Sugar for security reasons but not required)

5. When invoice is paid via Payment Processor, invoice status in Sugar is changed from paid to unpaid (real-time update preferred but this can also be a periodic batch update of invoice statuses between processor and Sugar)

6. When invoice is marked paid, it is exported to accounting system (again, real time preferred but could be a batch invoice export of all invoice mark paid that have not been previously exported.)

Most likely the integration would probably happen with one of these 'Big Boys' on the block for maximum functionality/compatibility but utiliting one of these is not required:

Payment Processors: Authorize.net, PayPal, Intuit Payments

Online Accounting Systems: Quickbooks Online, Dharma, Xero

Againg the question is what is the best (cleanest) solution at a reasonable price?

* Must be compatible with Community Edition.