Actually what are the differences between NAS and cloud services such as Dropbox? I would imagine: 1) For privacy, perhaps NAS is better? 2) NAS has more storage.
I tried to use a usb memory stick to share files between computers but I have these issues: 1. usb sticks failed to work after I did not unmount the sticks and pulled them out from the computer. Why sometimes it was fine but sometimes this caused corruption of the sticks? 2. Sometimes I lost the stickes and I have seen people leaving the sticks in public computers. For privacy and security reason, usb stick is not a good option for me. A reason I don't want to put backup drive in my desktop is that if something bad happens to the desktop (e.g. static electricity, fire, theft) everything in it will not be accessable.
Speaking of 20+ years worth of data... I am in kind of messy situation. I backed up laptops and desktops on multiple drives. When external drives and laptops storage became large, sometimes I copied back those drive contents into these new drives. Then sometimes I also back up these drives. So I have multiple copies of some files from Mac OS, Windows OS and Linux. This makes it difficult to find some files. Any suggestion on how to fix this messy situation?
My NAS box lives in my living room, 100% under my control
DropBox, etc lives "out there". Under control of someone else. Access subject to whatever internet connection speed is available at that moment.
USB sticks are,
at best, transitory devices. Used to sneakernet some data from one machine to another.
Never to be used for long term data and safekeeping, or any backup.
If one fails, so what...grab another and move on.
Backups should not be solely on the same desktop. Those are susceptible to all the same hazards as the original data. Ransomware, dead PC, fire, flood, theft, whatever.
A real backup scenario should be on a couple of different devices and types of access.
My last ditch fallback is data on a drive that lives in a drawer in my desk at work. This is for stuff classified as "should not lose, ever".
Stuff like scans of drivers licenses, passports. Insurance policies, birth certificates. Not my latest game save.
That gets updated every few months.
My house systems back up to the NAS every night, or every week, as determined by the system use.
As far as your messy data situation? There is no magic for that. And that is something we ALL end up dealing with sooner or later. Junk scattered all over.
You'll just have to devote some time to identify, consolidate, and fix it.
But if all that currently lives on a single 20 hard drive...good luck with that. Drives die. All of them, eventually.
You need to fix that.