I believe you just got bad luck with those drives. You should be able to RMA those drives if they were bought as new. I had a few drives which failed in a few months, and some that are running fine for 5+ years.

Depends on the NAS. Some of them offer native cloud option or access via the VPN.

Recertified drives are the ones which were in use and were returned due to issues. They usually get fixed if required and sold again. They usually have the additional limited warranty, which makes them a good option for lower cost.

Get an HDD for it. Internal or external, depends on you.

Alternatively, you may store it in Backblaze personal.

As a common source, obviously, internet archive is my choice. If I cannot find anything there, I start googling, so basically no favourite archive repositories for me.

You just check the best $?TB ratio and warranty time. That's really all the things you need when choosing the drive. Also, remember that there are only 3 brands Seagate, WD and Toshiba to look for.

Depends on your configuration.

If you do not need to passthrough the whole HBA to a VM for example, then, just go with the most convenient way for you.

I follow it for the most critical data, other data get just one copy (but those data is not important to me)

Even if it grows, if you found a good deal on Black Friday you just get it because the price is good nothing else.

I have offsite location as my cloud cloud backup. That's basically, it.

Not really much options there. Depends on the budget as well, but you won't have anything close to the price of backblaze personal.

If you have a good deal already, just have them. If there any good deals on Black Friday, then get them as well. You cannot ever have too much drives ;)