Sounds like you've got a good plan! You can save your gold for someone else, but I figured I'd chime in.
I don't have experience with any of your potential ZFS solutions, but I know FreeNAS lets you create an AFP share for existing zpools that is mountable for Time Machine. I don't know how permissions work though, as there is a Time Machine checkbox when creating the volume in FreeNAS. I'm doing stress testing on my 6TB HDDs right now, otherwise I'd create a new zpool and single volume and see if I can make CIFS shares and on it while adding Time Machine functionality to a single "Backups" folder or something. I could be completely wrong about this, though, so take my statements with a grain of salt.
Your PSU is way overkill for this setup. You could probably get by with a 500W. I had a 750W Corsair HX750 from my old gaming rig, so I just threw that in there, but your processor is pretty low power (kinda surprising actually!) and you don't have any graphics cards or anything. I'd recommend an 80Plus Gold PSU between 500 and 700W, but that's just me.
You could also save some money on RAM by just going with 32GB to start and adding another 2 sticks later down the line. I'm stuck at 32GB on my LGA1150 X10SLH-F-O and while I'd like more, it's enough for what I plan to use this machine for.
I'm basically running some Win8/10 VMs as general use boxes/virtual desktops, a 2012R2 DC running DNS and DHCP, a Splunk box on Debian 7, an OpenVPN server on Debian 7, a general Debian 7 tools/scripting server, and FreeNAS (8GB RAM reserved, 3x 6TB RAIDZ1 w/ 11TB usable passed through from an IBM ServeRAID M1015). I will be adding more stuff later, but I'm nowhere near max RAM usage and my CPUs are sitting idle probably 95% of the time. It's a production environment that I'm also learning on, but I'm not using 95% of the stuff ESXi has to offer.
I would have loved to have gone with Socket 2011, and looking back, it would have been a fairly marginal increase in price for massive expansion possibilities in the future... but I suppose I'll just build another box if it ever gets to that. Not for quite a while :)
Hope this helps... I got a little carried away.