I do however think that your questions are better asked at the FreeNAS forum. This forum has a lot of people knowledgeble in how Nextcloud works, but you will find more/better help about FreeNAS specific questions there. With luck, you might even get help from the creator of the plugin you are using.
If you use the server-side encryption of Nextcloud, this will mess up everything. If not, it can work, check also the howtos on how to change the data folder, it could be required that you change the data-folder location in the database as well.