External SSD Boot Drive on 2012 Mini?

You can do that.

You can use either the Thunderbolt port, or use USB3 instead.

Most folks might think "thunderbolt is faster", but the differences between it and USB (with the proper enclosure or dock) are all-but-negligible.

You can get a USB3 enclosure for as little as $30, such as:
http://oyendigital.com/hard-drives/store/U32-M.html

… or something like the new Firmtek enclosure ($99):
http://www.firmtek.com/seritek/miniswap-u3/

The latter is very fast, but the $30 one isn't really that far behind.

As for the SSD to put inside -- you'll have to pick that on your own. I have an Intel 520 series that seems to be doing fine.

 

I don't know about the Corsair drive either, but I'll _guess_ that almost any SSD you use will work well enough. Some may be faster than others, but almost all should work fast enough. Almost any SSD will make a user quite happy!

Does your internal drive have the 500gb or the 1tb HDD?

If you're going to kee a "2-drive setup" (two separate drives, not "fused"), you might consider partitioning the internal HDD.

Make the "first" partition the same size as your SSD.

Now, use either CarbonCopyCloner or SuperDuper to clone the contents of your boot SSD back to the "backup boot" partition on the HDD. The remaining partition of the HDD can be used as you wish. (again, if you keep something valuable on it, it's advisable to back that up, too!)

The idea is to have a second, bootable copy of the OS close-at-hand. Yes, it "uses up" free space on the internal drive, but it's always wise to keep a second copy of your OS and account/data files nearby.

Periodic "incremental backups" (again using CCC or SD) go _very_ fast once you have this backup scheme established.

I've seen advice from others here at MR that it's a good idea to do frequent backups of an SSD -- because when an SSD fails, it tends to fail catatrosphically. That is to say, it's possible to use data recovery software to scavenge files from a failed HDD, but much more difficult with SSD failures (due to the nature of how they operate).