My plan was to install Proxmox and run TrueNAS on top of it
Proxmox runs ZFS natively already so there's not much reason to bother with TrueNAS IMO. If you need SMB shares and that sort of thing you can run a container and mount the ZFS volume into it.
I currently have 4x900 GB 10k SAS Dell Enterprise drives but I intend to bump that up to 10x900 GB over time. I’d like to be able to add these without much hassle
If you want to easily add drives later on then as far as I know the only good option is the controller in HBA mode with unRAID in a VM. Hardware RAID or ZFS don't make adding drives very easy.
I’m wondering if using ZFS with the RAID controller in HBA mode will be more worth it than a dedicated RAID setup
I think ZFS RAID with HBA mode on the controller is worth it vs traditional hardware RAID, it's more portable, less reliant on hardware.
And if I’m using a RAID setup, should I go RAID or unRAID? If I go RAID, is RAID 01, 10, or 60 a better option here?
With 10 drives I would probably do ZFS RAIDz2 if this was my setup. (RAIDz2 has 2 parity drives like RAID 6).