I don't have access to a customer import that I can find, but if I did I'd be violating terms to give it to you regardless as that code is not mine to share but rather paid for by others. Maybe I'll write a simple import for you at some point but I'd rather not get into an infinite loop on this request.
Point I was trying to make when responding to your initial question and maybe I wasn't clear enough was: I don't see eConnect as the problem, it's your experience with C# that seems to be more the issue. If you don't have experience with passing parameters to procedures or querying SQL directly from VS or using data sets or arrays then I think it's tough to start where you are starting. Understanding deployment, ini files, includes all part of the process here.
That said, I'll see if I can write something simple but if I'm putting in community time today it will be testing sales tax calculations for Richard.