Yes you can do that.I have been debating installing a ssd inside my mac mini. Now that I see this I want to go the external ssd route. So that I am not confused I can buy an ssd, put it in a external case, plug it into usb/thunderbolt, and run it as the "startup" drive with the mac os on it just like if it were installed inside of the mac mini?
It is as easy if your HDD is on the upper bay. You just need to buy the lowerbay sata cable and slide the SSD inside without taking the whole thing apart.