This may be vague but hopefully someone can help me refine the question, but what I am looking for is perhaps ways/tools which I can test ecommerce/b2b functionality, like punching out using cXML, creating EDI documents, and testing them in a (ideally free for development)sandbox. Can anyone suggest anything?
In other words, you're looking for a free (ideally) data translator.
You could download the Jitterbit Community Edition (Jitterbit)
You could also use BOTS for EDI: BOTS
Or Talend (Talend)
Without knowing full scope of what you're trying to do, it's hard to point in the right direction. If you want a commercial data translator that you plan on building out an integration architecture, look at Liaison's Delta and ECS (Liaison)