At the moment have a bunch of seagate and WD xTB drives interchanged for backup at various stages.... But need something more robust going forward.
You have many, many options. You can use a DAS like a multi bay Thunderbolt enclosure or a Drobo so that you can have all your data in one location. You can set them up with some redundancy to protect you against drives that fail.
The benefit of a DAS over a NAS is that it
can be much faster. Gigabit ethernet, which is most common in home networks, top out at a theoretical limit of about 125MB/s. A DAS connected via Thunderbolt or USB 3
can achieve speeds several times faster. I put emphasis on "can" because actual speeds can depend on many factors including type of array that you run, type of drives you have in the array, whether or not you have a cache, etc.
A NAS has the advantage of easy access by all the computers on the network. But you can easily share drives connected to your Mac Mini so that other computers on the network can access your DAS too. IDK if there is any overhead that would severely impact speeds, but I suspect that even if there were, it would be pretty minimal. As mentioned earlier, many modern NASes can run applications such as Plex and do things like transcode. One usage example would be, having a NAS with al your media stored on it. Then having media players such as an Apple TV connected to all the TVs in your home which can access and play the stored media at will. This example would be more cost effective than having to get a Mac Mini for each TV in your home. Plus, it would probably more power efficient.
Whatever solution you end up choosing, I highly recommend you set it up with redundancy to protect against at least one failed drive. Over the years, I have had many hard drives go bad on me and I have never lost any data that were protected by redundancy. Another thing that I have found to be
extremely useful is dynamic expandability. I started off years ago on a 4 bay Drobo with four 2TB drives and slowly swapped them out one at a time as I needed more storage. Today, I have transferred all those drives to a 5 bay Drobo which has five 8TB drives. It grew with me as my storage needs increased (I know... I'm a data hoarder...).