Although it is not yet announced on the project page freenas.org, the final version FreeNAS 8.3.1 is already available for download on the Sourceforge account of the FreeNAS project. The main change is the support of encryption, which however only works with 4K block size (Release Notes FreeNAS 8.3.1). As always since FreeNAS 8.2.0, the plugins and plugin jail do not need to be updated, but can simply continue to be used. FreeNAS 8.3.1 can be downloaded for x64 and x86 both as an update and as an ISO for new installations on Sourceforge. In my experience it is worth to wait a few days, often there was a following release with patches (PL1), which fixes possible bugs.
If you are looking for inspiration on how to build your own FreeNAS system, you can find it in my Shopping list for FreeNAS on a HP N40L/N54L maybe inspiration.