"One more quick question, if I decide to go this route, should I leave to OS on the internal drive, move it to the external SSD, or just move my applications to the external drive. I'm looking to speed up applications, such as Lightroom, and photoshop, and am not really concerned about boot up speed."
My suggestion:
If you have two drives (one HDD, one SSD), you ought to have TWO bootable systems. What this means is that if you ever have a problem booting from your main drive, you can instantly switch to the other drive, boot from it, and go to work to resolve whatever problems you have.
EXAMPLE:
Lets say you get a 128gb SSD, a common size these days.
In this case, I would create (at least) two partitions on the factory-installed HDD. The first partition would be 128gb or so -- this will become your "SSD backup". You can then use whatever is left for "general storage space", such as video, mp3 files, photo archives, etc. These are less-often-accessed files that you probably would not normally keep on the SSD because of space considerations.
Your SSD should contain the system, your apps, and of course your account (user folder). HOWEVER, in order to preserve space on the SSD, you may need to relocate some files you would normally keep in your user folder to the general storage area of the HDD. Again, this is to preserve space on the SSD.
Once you have your system, apps, and user account set up, use CarbonCopyCloner to clone the contents of the SSD to the backup partition on the HDD. Now you have a bootable and instantly accessible backup of your stuff (not including the files on the "general" partition). You can use CCC to periodically (and incrementally) backup your SSD to the backup partition. Do this, and you are "protected" -- at least more than most folks.
You might also want to consider a -third- drive, to serve as a backup to the "general" partition on the HDD. Remember, if it's something you value, you need AT LEAST TWO COPIES of it on different drives.
Insofar as opening the Mini is concerned, that is up to you. I left mine alone. Too many stories right here on MR from folks who "thought they could do it", and ended up breaking something. I may get into it someday, but until the warranty's up, I'll leave it alone and use an "external boot solution" as I pointed you to earlier. You will lose next-to-nothing insofar as speed is concerned. It works for me.