This is a very, very bad idea.
SSDs are permanent flash storage, yes, but that doesn't mean you can leave them unpowered for extended periods of time.
Without a refresh, electrons can and do leak out of the charge traps that store the ones and zeroes. Depending on the exact NAND used, the data could start going corrupt within a year or so.
HDDs suffer the same problem, though less so. They can go several years, possibly a decade, but you'd still be risking the data on the drive but letting it sit unpowered for an extended time.
For the "cold storage" approach you should really be using something that's designed to retain data in such conditions, like optical media, or tape drives.
Yes and no.
Pending means the sub hasn't gone through to the home instance of the community. If you're the first subscriber, this means the there will be no inbound federation bringing the content from that community to your instance.
If someone else on your instance has already successfully subbed, the federating is already occurring, and your instance will be receiving the activity as it comes in.
Your instance will then show it to you, both in your subscriptions and in general, even though the sub is pending.
If your sub stays pending, you may have to unsub and resub to get it to work. If no-one else on your instance has subbed either, then the activity will continue to not show up for as long as it is pending.