eCommerce for start-up Customer orders and Payments and Supplier Orders and Payments

If you take the overall business process flows and lay them out a bit you have two of them - one for your order to cash process and one for your procure to pay. They would look something like:
1) Sales Order, Schedule, Ship, Invoice, Cash
* or maybe collect cash up front so no invoice
2) Purchase Order, Receipt, Ship, Payment

Then you add your specific requirements to these:
1) You want the customers to order via ecommerce (B2B model with security most likely)
2) You would like the Sales Order to generate the purchase order (something to happen inside of your ERP and not usually in the ecommerce module)
3) You want the suppliers integrated into the process (could be in your system or integrated messaging)
4) Other requirements - such as shipping documentation (whose?), dropship directly to customer or via 3PL or from your site?

From the above I do not think a custom ecommerce module is required. What is required are two business processes with integration between them along with the ability to integrate. Certainly Microsoft Dynamics would support this - I'm guessing a number of ERP systems would.

Bob Scarborough