Before upgrading to the SSD, try the RAM upgrade if the cost isn't too great... in that with more RAM installed, the hard disk drive would not require as many read-writes as virtual memory while handling larger files or complex processor activity where swap files or temp files have to go into VM at slower disk drive speeds than the bus speeds on the logicboard. And the unit may be a bit cooler with less fan noise, until it heats up.
The capacity of the 1TB HDD is tempting and a value for the money in several ways; so long as you acquire more than one method of extensive backup of your work. And also consider a clone of the OS on an external drive device enclosure that supports booting your Mac, as a real backup outside of TimeMachine methods.
A value in upgrading from the larger HDD to a solid state drive, and retaining the relatively new HDD with a partition for a complete clone of your Mac's system, could be good if managed carefully.
There is a limit in length if cables are utilized to access an external hard drive or other components at distance from the main computer unit, so if you had to boot and run from an external drive that has a self-powered enclosure and a clone (or main system) you'd want to carefully not marginalize by overextending this limit. Maybe have an SSD inside the Mini and a capable enclosure with the large drive outside.
Should you check into the cable limits to be sure the microphone and other components can be at reasonably good distance to minimize sound interference with your recording, and if needs be, consider inquiry into the basics of constructing a sound minimizing box that has ventilation & access door to handle the Mini as needed. Just so long as nothing near the computer can retain heat, conducts cooling air flow, it can be done. So long as the materials do not block wireless BT keyboard & mouse. Or run USB cable within limits.
{A thought in the above, concerning use of heat conductive electronic modules that are in use in portable refrigeration, as adapted to cool a vented enclosure for a computer (without liquid, etc) to make a cool box?}
The SSD is a good idea, and some replacement upgrade brands are maybe a notch above the rest. I'd seen where OWC has some quality builds but I have never bought anything from them. There is even a retro-fit SSD for older PPC Mac desktop and portables to get more umph out of an iBook for example. Maybe.
Best of luck in your studio work.
Good luck & happy computing! 🙂
