Filesystem question

Hello /r/linuxadmin!

This is my first post in this section, but I really appreciate all the feedback I've read on this subreddit for years. Basically my question stems from what you recommend to manage a filesystem.

I have a server with 24GB of RAM and 4x2TB HDD's. I want to create a iSCSI or ZFS based filesystem to use with a virtualization cluster. I wanted to link it up with the Proxmox software to create allow high availability (network storage is required).

Should I use something like FreeNAS to deploy such a solution with a software RAID, or should I buy a RAID card and do a RAID-10 for my setup? The reason I like ZFS is because I can add SSD's for caching, and doesn't require more purchasing for a RAID card.

Please let me know your thoughts!