I would advise you to "prep and test" the new drive BEFORE you attempt to install it into the Mini.
Use either an external enclosure, or a USB3/SATA docking station, or a USB3/SATA "dongle" to make the connection.
Connect the SSD, and use Disk Utility to re-initialize it to Mac format -- HFS+, GUID partition map.
Now use either CarbonCopyCloner or SuperDuper to clone the contents of the internal drive to the SSD.
Now, do a "test boot" by restarting. As soon as you hear the startup sound, hold down the option key and KEEP HOLDING IT DOWN until the startup manager appears. Then select the new (external SSD) drive with the pointer and hit return. You're looking for a "good boot" from the external. To be sure you're actually booted from the SSD, go to the Apple menu and choose "About this Mac..."
Once you do the drive swap, use the enclosure or dock to house the removed HDD.
CCC is FREE to download, and it's FREE to use (fully functional) for 30 days.
SD can do a "full clone" forever without registering (you do have to register to do incremental backups).