I could see using the Zotac system if you built a box and then put it in the closet never to use it for more or touch it. But it seems too limited (and very slow) if you want any kind of future-proofing to be able to upgrade with later. I would look at the ASRock system myself. The ASRock can use 8GB of RAM vs. 4GB in the Zotac. Also The ASRock can support USB 3 ports which are useful for external storage. You would probably have to look in to getting something like a PCI-e 1x SATA card for more ports if you wanted to use more than the 4 hard drives it can support with the built-in SATA ports on-board.
As you noted, the N3700 has issues with running without a monitor.
AsRock N3700-ITX doesn't boot w/o DVI