All the Samsung SSDs are pretty good and highly thought of, and I have one. I also have the SanDisk stand-alone (like the T5 and T7, but in a different shape), that don't require an enclosure.
If the size is not too much of an issue, then internal SSDs, typically in the normal 2.5" inch size (like the ones that often come in laptops) are cheaper, including the cost of an enclosure, and can be very fast, with the added benefit that you can swap them out. There are two types of these: the 2.5", whhich look like enclosed drives; and even smaller ones, "NVME" types, in that they are not enclosed, and are long and thin. Both of these kinds will fit into enclosures, meaning you can swap them out for an upgrade or replacement yourself. I also have several enclosures from Other World Computing for both these types, but particularly for the 2.5" SSDs, and they have also performed flawlessly. The 2.5" can also be inserted into docs, similar to normal, spinning, 3.5" hard drives. I'm a big believer in future-proofing myself, so if I can afford it, I go for Thunderbolt 3 or at least USB C enclosures or drives, but if speed is not that important, everything below those kinds of connections, while slower, also cost less.
While I love my SSDs, and the prices are dropping all the time, for bigger storage, say, 2 or 4 or 6 TB or more, normal, spinning 3.5" hard drives are really cheap in comparison, and like the SSDs, also dropping in price all the time. This also means you can have more copies; I typically have three copies, at least, of every drive.
Finally, it's generally not that difficult to swap out the internal drives of earlier Mac Minis, depending on its age (later ones have the drives welded to the logic board), in which case you can solve at least one of your problems. I have my catalog on my main, internal drive, and it's backed up to the drive where I keep my photos.