Not sure about the RAID setup but what you want is very possible with ESXi.
PFsense in one virtual machine, ubuntu server on another with a SMB or NFS file share setup.
I run a sever for my home automation and wanted to run PFsense so It made sense to have them on one box. I run my with a i5 3570 but it is barely getting utilized. Pick up a intel 4 port gigabit NIC off ebay for ~30 bucks and you will be ready to roll.