I agree with the cautionary tales regarding digital disks either CD or DVD. I think that magnetic media are good standbys. Hard drives are relatively inexpensive. It doesn't cost that much to have an external hard drive full of digitized family treasures stored in a secure part of the home or exchanged with a friend.
Of course, you should also keep the primary sources, documents, photographs, slides, etc. in a 'cool, dry, place'.

I transferred my family's audio tapes to digital media a few years ago. They were all in the range of forty years old. There was considerable quality differential between brands. DECCA tapes seemed as original. The London FFRR tapes of Gilbert and Sullivan required to be 'baked'.

As for 1 TB versus 500 GB hard drives, the preference goes to the more recently manufactured. The increased capacity may come from extra platters or extra density. What you care about with magnetic storage is not so much the density as it is the engineering and the quality of manufacture. Magnetic media involve a small magnetized area which is surrounded by a 'domain'. There are calculations made during design to assure that it can't be changed without a considerable outside force. When I buy a drive, I plug it in and leave it on for a long time, sometimes take it to work and just leave it there as an adjunct drive. This gives the little heating faults a chance to work themselves to the surface and fail in the first three months. If it still works, then I load it up with my precious data.

One nice thing about the 'portable drives, which are just hitting the 1 TB size- since they are powered off the USB, if you have any kind of power backup on your desktop, or if you are using a laptop with a decent battery, a power failure at the mains will not cause a powerfailure in the drive, so long as the computer is still running,whereas if it plugs into the wall, power failure there will upset that data transfer. The portable drives take up a lot less space, store better, and are easier to transport, as many of them will fit in a shirt pocket. They are no less reliable than the larger external drives. You pay a modest amount extra for the portability and they spin at a slower RPM, which means they don't transfer data as quickly.

Still it is scary. Having hundreds of gigabytes in one place. Avoid putting it through a procedure where you're holding it with one hand or regularly moving it about.