How many displays/monitors can a Mac Mini 2012 support?
From Everymac... http://www.everymac.com/systems/apple/mac_mini/specs/mac-mini-core-i7-2.3-late-2012-specs.html

2nd Display Support:    Dual/Mirroring* 2nd Max. Resolution:    2560x1600*

*This model simultaneously supports 1920x1200 on an HDMI or a DVI display (using the included HDMI-to-DVI adapter) and 2560x1600 on a Thunderbolt or Mini DisplayPort display or even a VGA display (with an optional Mini DisplayPort-to-VGA adapter, which is compatible with the Thunderbolt port).