I run a nearly identical server at home (the Mac Pro that is, not the massive RAID). I made the decision to install FreeBSD when I set it up and haven't regret

I run a nearly identical server at home (the Mac Pro that is, not the massive RAID). I made the decision to install FreeBSD when I set it up and haven't regretted that for a minute. The hardware is actually lovely, right down to the literal nuts and bolts. Just stay away from the Apple software ecosystem and you'll be fine.