Well, if you insist and using inferior products, you will probably have to invest the time yourself to learn how to script them. There are many, many more solutions already built for Excel than Numbers, and Numbers, like Pages, has limited scripting support, and is a PITA to work with.
I'm ready to help with Excel, but I just don't have the time, or inclination, to help with Numbers. Of course, there may be others who are.
Have you tried searching the Internet? Your use case is very common, and I'd expect you'd find a script somewhere for appending CSV data into Numbers.
Perhaps my response was a bit strong, but I stand by the facts: Apple Numbers is MUCH harder to automate and script than MS Excel. Excel is head-and-shoulders above Numbers.