Hi Keith,
Welcome to the FreeNAS community.
Know that as powerful FreeNAS can be, it also means that you can shoot yourself in the foot with a bigger gun. Better to take a maximum of time planing and trying in a test environment where you are ready to loose everything than learning the hard way and loosing your data for real.
As a first step, you can post a description of your setup. Typical errors are the use of RaidZ1, not enough RAM, running FreeNAS as a VM without all the required precautions and activation of features that are more problems than solutions like deduplication.
Enjoy your setup,