"My question is, do I have to format and install OSX on the SSD before installing it?"
It's not imperative, and things may go ok for you if you don't, but still I recommend that you do.
Reason:
If you wait until the new SSD is inside to do the installation, and discover that you're having problems, you _may_ have to pull the SSD back out again to solve them.
If you get the SSD "up and running" BEFORE you install it, you already know it works "in your hands".
A handy and inexpensive gadget that will make this easy is a USB3/SATA "docking station". You can find these for $25-30 over at amazon. And it will come in very useful in years ahead if you acquire another "bare" hard drive (or two).
Suggestion:
- Have the dock at hand
- When the new drive arrives, put it into the dock, power everything up
- Initialize the SSD with Disk Utility
- Use CarbonCopyCloner (free to download and use for 30 days) to clone the contents of the internal to the new SSD. CCC can also clone the recovery partition.
- DO A TEST BOOT BEFORE THE SWAP. Restart, hold down option key after startup sound and KEEP HOLDING IT DOWN. When you get to the finder, select the SSD with the arrow key and hit return. The Mini will boot from the docked SSD. When you get to the finder, verify that you _are_ booted from the SSD in "About this Mac" under the Apple menu.
- With all this verified, now is the time to "do the swap".
WARNING:
If you install the SSD into the Mini along with the existing HDD, and then boot to the recovery partition, and then attempt to use Disk Utility,
DISK UTILITY WILL TRY TO "MELD" THE TWO DRIVES INTO A FUSION DRIVE AUTOMATICALLY.
(shouting intentional)
If there are any files on the HDD that you want to preserve, you must back them up to an external drive first!
If you want to keep the two drives "separate" (not "fused") after installation, you must NEVER run Disk Utility from the recovery partition, it will keep trying to repeat the above process...
