I am interested in how this is working for you, since I am looking at moving in a similar direction myself.
In general, I'm pretty happy with the purchase. From a hardware standpoint, there hasn't been a lick of trouble -- though that other thread is a reminder that I really should check the drive temps. I haven't looked at them at all. I have the 4 drives in a Z2 array (2 drive redundancy). Aside from the power supply issue, everything went into the case just fine, but it's a *really* tight fit for the mobo. There is not a lot of space. The fans are quiet enough that I've never noticed them while working in the office. The drives make more noise than the fans, IMO, but I have tinnitus, so maybe I just don't notice.
On the software side, it's been a mixed bag. The two sore points for me: 1) configuring it to use as a print server, and 2) crashplan.
1) Setting up a jail with CUPS is trivial. My printer has a wireless network option, but a) it's finicky at best, and b) it can only be configured wirelessly if the wireless network is configured in an insecure manner, so we use it with USB. Unfortunately, no-one seems to know how to get FreeNAS to provide permissions to access the USB device to the non-root users of a jail. FreeNAS appears to configure their jails just slightly different from stock FreeBSD, so that the guidelines for FreeBSD don't work. The response from FreeNAS contributors with respect to USB devices is along the lines of "FreeNAS is only for storage, the developers don't intend it to be used for things like that, so won't spend time developing it." Which, of course, isn't how FreeNAS is marketed. But anyway. This is solvable, I just haven't spend the time to do so, since my Linux desktop is doing an adequate job for the time being.
2) Crashplan. Ugh. Yes, there is a crashplan plugin. I have had nothing but problems with it. There are loads of people out there who have nothing but problems with it, and their searches for assistance all seem to be met with "but it works flawlessly for me." Well, it doesn't. Code42 appears to not have any backward compatibility in their client software. If the client software isn't the same version as what's running on the server, the two won't communicate. The FreeNAS crashplan plugin was packaged with an old 3.x version of the client software, and current version is now 4.x. It's supposed to auto-update, but the auto-update failed. I have tried a) re-installing the plugin, b) installing an x server and vnc server to run it non-headless, c) installing a normal jail with linux compat and installing the crashplan without the plugin, and d) giving up. I will not be using crashplan. Instead, I'll just rsync my linux desktop, and install the rsync-based
iBackup on the macs, and let ZFS do its snapshot magic. I'm still not settled on cloud storage yet. rsync.net's ZFS replication is nice, but extremely expensive -- they claim it's due to enterprise-class support, but I don't need enterprise-class support, I just need an end-point for a ZFS send command. I'm currently looking at Backblaze B2, with duplicity.
Other than that, I'm happy on the software side, too.
The plex server plugin works just fine. I've had no issue streaming/transcoding H.265 videos to an ipad. Setting up jails, storage, users, snapshot schedules, etc is easy too. It would be nice if there were a simple button to set up recommended snapshot intervals for a data set, but that's a pretty minor point.
The majority of the issues I've had have been 3rd party integration. For example, I needed to tell her mac book to index the NAS drives, so that she could use Spotlight. And I couldn't use my regular gmail account for the SMTP settings, without turning off security settings (so rather than set up another gmail account, I signed up for an SMTP relay service).
The only thing I wish I had done was max out the memory supported by the mobo, but that's really a temporary issue. I'm using the server evaluate CRM systems for the theatre, so I have a couple of jails set up running apache/wordpress/mysql installations. Once we make our choice, one of those will go away, and the other turned off except for dev/testing purposes.
From the standpoint of using the box as a NAS, it's been a set-n-forget operation, just as I'd hoped. It just sits there, ticking away.