Ansible-NAS will run against any Ubuntu box, a Raspberry Pi 4, or even a VM if you're just testing things out. The hardware you pick for Ansible-NAS depends largely on what you intend to do with your server - and is very much a "how long is a piece of string" type question.
📄️ Migrating from FreeNAS
FreeNAS uses ZFS as it's core storage filesystem. ZFS on Linux is supported natively in Ubuntu, so importing FreeNAS zpools is easy.
📄️ NFS Exports
Ansible-NAS uses the awesome geerlingguy.nfs Ansible role to configure NFS exports.
📄️ Samba Shares
Ansible-NAS uses the awesome bertvv.samba Ansible role to configure Samba - check out the project page for the many different options you can use to configure a share.