Hi DB,
The ECF sends out automatic emails for store purchases. And depending on the payment gateway and merchant account you have set up, you should receive a second email from your bank.
For additional billing needs, there will be some customization in the back-end admin site, or the ECF Commerce Manager.
Mediachase offers our own Professional Services and have done integrations with a number of our customers with ERP systems such as Dynamics Navision and then you would have all the functionality that you need. If interested in discussing this more, please contact sales@mediachase.com.
If you want to do any custom payment gateways yourself, it is highly recommended that you purchase the full source code license -- http://www.mediachase.com/catalog/productinfo.aspx?id=106
To answer your second question regarding localization, if you want mulitiple languages on your site, it is correct that you will need to copy the objects (categories and products) from one language using the "Copy" feature in the ECF Commerce Manager. For more information, please refer to -- http://www.mediachase.com/documentation/ecfv4doc/ecf41_localization.pdf
Hope this helps!
Mediachase Software