Late to this post, but it seems everyone is mostly posting here regarding the Dell FS12-TY C2100 (not the one that stacks the drives vertical, this is 4 hard drives across, 3 down. I feel comfortable with this platform, but just to re-iterate what others have said, dump the H700 like it's the plague. Very bad for FreeNAS, doesn't work at all, I was able to reproduce seg-faults just by removing a drive. Configuring an H700 with Raid0 drives is a recipe for disaster. Use the H200, flash it first following my step-by-step tutorial here:
https://forums.freenas.org/index.php?threads/how-to-flashing-a-dell-h200-with-a-dell-r610.32919/
I did this on an R610, when my C2100 arrives I'll have another H200 to test with and flash. If the C2100 won't take it I can use my spare desktop used in those instructions. My configuration will be 2x8gb usb for OS, 8x3tb in a stripe/mirror (12tb usable) and 3x512gb Samsung SSD pro in Raidz1 (1tb usable), 64gb ECC mem and 2x5630 CPUs. I will use the stripe/mirror for hot replication backups and SSDs for NFS mounts and some live VM images. Previously I ran FreeNAS on a Dell R610 for about 72 hours running disk i/o and build worlds and saw good performance. No hiccups after going to H200. I'll work the C2100 for a week or so before putting into use and will post some stats/experience when done.
Like the OP and others, I also get all my hardware from Deep Discount Servers on Ebay. They have a great inventory, ship quickly and are nice to deal with. Do yourself a favor and get spares as well. I typically go with extra mem, 2 extra power supplies (I've found PSes are the most likely fail point), and a spare chassis with CPUs. I hate moving CPUS from chassis to chassis and spending an extra $500 for a duplicate server (If you're going used), is definitely a good investment.
Let me also give a sales pitch for a backup application. I currently have 3 VM nodes (Essentials) and 2 HyperV nodes. I searched and tried several packages, you can spend some nutty cash here if you want, but I certainly can't afford that. I initially tried one that was $99 a node and $49 for the backup server called Cloud Backo. They have very good support, but when running this and inspecting the data this software creates 1000s (and I mean 1000s) of tiny 10mb files per VM, the format is completely useless and you must restore the VM using their software. Speed was not all that great, it did support compression and CBT (not for Free ESXI). I determined though it was not the backup software for me. <salesmodeon>I ended up finding a package called VMExplorer by Trilead. The software/license is $790 and gives you unlimited nodes for both ESXI/HyperV. It has a VM agent that supports server to server backups and replication. You can also backup to anything the backup server sees, local and remote HDs. Local backups and replications can also be incremental, it also uses CBT. What I like about the backups is in looking at the data files they are pretty much the same VM images/files for the VM copied (after snapshot) to the local HD. IE, you can copy these files over to a VM store and spin up a VM from them. They also have an explorer that you can double-click on the hd image and browse through the files (Some unix platforms not supported) and restore single files. You can also opt to put the backup files in compressed form (gz) understanding you lose the ease of file-by-file backup. However, I've unziped the images to a new directory and they can then be browsed again. The images on a server-to-server backup can be used to create a new VM direct, Replication does that too putting a (replicated) tag in front of the VM name. I can't say enough about this package, it definitely is worth looking at if you have a mix of ESXI/HyperV servers. Even just for ESXI is very cost effective compared to some of the others. The reports html/email as well as general GUI are very polished.</salesmodeoff>