I can't help with the package creation part of your post, but thought I'd mention that one of the pfSense developers is working on the return of vnstat. A promising screen capture was posted the other day in this post of the graphing, but the caveat is that the developer working on it doesn't have a timeline for completion, and the level of effort depends on workload of other more important items.
But there is work in progress to bring vnstat back to pfSense. :)