Minimum display resolution for macOS Sierra on Mac Mini (2011 or later)? I'm considering getting a secondhand Mac Mini (2011 model or later) for use as a media and backup server. 

Most of the time it won't need a screen attached to it, but I'll need one in order to initially set it up, and perhaps for occasional maintenance or upgrades. I don't currently have a monitor or TV so I'll need to get hold of some sort of screen for it and I'd prefer it to be both cheap and small. 

I can see monitors on sale in the 8" to 10" size range, with resolutions from 800 x 480 to 1280 x 800. What is the minimum resolution this screen needs to support, to be compatible with either the Mac Mini hardware or macOS Sierra itself? I can't easily find this information on the Apple site or elsewhere. 

It doesn't have to be comfortable to use, just possible - i.e. the macOS installer must run, standard dialog boxes must display on the screen, and so on. I'm aware that 15" and 17" LCD screens are available for next to nothing, but I really want something smaller due to limited storage space.
The minimum resolution supported is 640x480. To get to this resolution (at least on my monitors on Sierra), when I'm in display preferences, I have to Control + click on "Scaled". This gives every resolution option, not just the main ones Apple thinks I want to use.