No reason why not. May be a little power-hungry depending on the spec but if you already have it go for it. FreeNAS (now TrueNAS) is the usually suggested OS to run: www.truenas.com/freenas/
Since you have 4 HDD slots probably run 4 disks in a RAID 5 so think of how much space you need. RAID 5 is n-1 so if you have 4x 10TB drives you will be left with 30TB of space before formatting. You can calculate here: www.raid-calculator.com
Then either mirror the SSDs for OS and caching or just use one. Depends on your budget really.