Having built complicated storage systems during work hours I had a strong urge to build a home NAS. What stops me is that I have this Documents directory on my laptop, which was salvaged from another disk that failed about three years ago, and served for 11 years prior to that, and some documents were copied to it from a PC I owned before then... and going farther back doesn't really make sense as none of the documents would be really relevant / authorities at the time couldn't deal with digital copies of documents, so, storing them made no sense.
So, in the end, I just keep them in the Documents directory. Some, most commonly used are also in my email. That's it.
I've personally been asked by authorities to produce documents that are 30+ years old. It's a bit surreal and I wonder if they could even authenticate them...
I only have a handful of documents that are about that age: my birth certificate and high-school graduation diploma.
Here's an interesting aspect of these: I did lose my college papers a while ago, and when I asked my college if they can produce a copy, they told me that they keep their records for just seven years. So, they had nothing. The high-school I went to doesn't exist anymore. So, if I had to recover my high-school-related papers, I'd have none. But, if I really had to, I could recover my birth certificate, as those don't seem to have an expiration date.
Anyways. In terms of storing digital copies, very little of that is relevant. Even ten years ago most authorities wouldn't be able to accept digital copies. Even today, the municipality of the city I live in won't take digital copies. There's no process through which I could have a digital copy they would recognize.
So, I need to keep hard copies. And the digital copies? -- well, they are perishable. I keep them for convenience, because every now and then I run into some situation where they are accepted. But losing them won't be a big deal as I can always make more of those. So, I don't need any exceptionally reliable storage requirement for the digital documents. It's more like a cache, which can be eventually retired.
I have to keep hard copies anyways. Plenty of places don't take digital copies and have no process through which they would. So, digital documents are only a convenience for the rare situations when someone will take them. And if I lose them -- well, I'll just take another picture.
So, in the end, I just keep them in the Documents directory. Some, most commonly used are also in my email. That's it.