Thank you very much for your answer :)

You are right about the csv format, I was thinking in a excel.

I thing that storing my metadata keys in an array rather than a hash it would be better, the problem is that I don't know how to asociate the metadata in the array with the values without doing it with a hash.

Your third and fifth points look like very interesting, but I am "noob" and i don't know how to do it :(