The recommended rate for RAM to TB of storage is one, so for every 1TB of data they recommend you need to have 1GB of ram. Not sure how relevant it actually is since I have a lot more ram than storage on the server, but just something to note.

Virtualising ZFS on top of ZFS is generally not supported and can cause issues. I run TrueNas baremetal and run a lot of docker services in TrueNas itself, you can also run VM’s on TrueNas. I know some people virtualise TrueNas in Proxmox, but the only use I see is to host something in a VM on proxmos that you cannot really run inside a TrueNas VM. The thing with TrueNas is that everything is either stored in the datasets or in the config file. The latter can be backupped pretty easily.

I have both a TrueNas server and a Proxmox box with OPnsense running, Proxmox is very nice I just don’t see a reason to run TrueNas inside Proxmox.

Not the person you responded to, but personally I just went Truenas scale on baremetal and it worked really well. Currently they also work with docker so setting up additional apps is really easy as well.