Dual and triple non-TB monitors on a Mac Mini late 2012 (Macmini6,2)
Dual yes natively, Triple not without USB adapter one of the displays.
You can look over these two articles:

Apple Thunderbolt Adapters: Frequently asked questions (FAQ) - HT5309
Thunderbolt ports and displays: Frequently asked questions (FAQ) - HT5219

[Item 23] of the HT5219 article is most relevant3:

Q23. How do I connect my Mini DisplayPort monitor or monitor using a Mini DisplayPort adapter to my Thunderbolt-equipped Mac when I have other Thunderbolt devices connected?
When connecting a Mini DisplayPort display or a display using a Mini DisplayPort adapter to a Thunderbolt peripheral (except as described in question 24), make sure the display is connected at the end of the Thunderbolt chain. You can use only one Mini DisplayPort device in the Thunderbolt chain.
Note: Systems with more than one Thunderbolt port, like an iMac, can have more than one Mini DisplayPort monitor or monitor connected with a Mini DisplayPort adapter connected as each Thunderbolt port can support one Mini DisplayPort display.

Item #18, footnote 4 explains that you only get two monitors with the Late 2012 Mac Mini using Thunderbolt and/or HDMI. To add a third, you'll need a USB adapter for the one that has the fewest pixels / slowest refresh rate requirements. Perhaps you can get a newer (or used but more capable) Mac when it's time to run the Wacom Touch.

MacBook Pro (Retina, Mid 2012), MacBook Pro (Retina, 13-inch, Late 2012), and Mac Mini (Late 2012) computers can use an HDMI-compatible device on it's HDMI port while using one Thunderbolt display, or they can use two Thunderbolt displays.

You'll want to use either a thunderbolt to the exact adapter for each monitor rather than chaining two adapters together if at all possible.