I am not sure if you are planning on using real used cocoa bags but I would caution you on this. I purchased some from BurlapFabric.com expecting to do the same - decorate my store and it was a HUGE mistake. Since the fermented beans are shipped in these bags...they stink to high heaven. There was such a bad smell from the cocoa bags that I had to store them in my garage until I figured that even washing wasn't going to save them. I ended up having to toss all of them.
They were super cool to look at and seemed like they would be great decor but in the end I was told from other chocolatiers, the smell in the bags is pretty common and does not come out.