The OP already has the online storage covered. This is regarding using HDD's for offline (not spinning) storage. Even if they're not being accessed and are physically separate from the primary storage, you still are subject to wear (spinning platters) and things like power surges.

Putting the dries back into their orignal enclosures, or perhaps an "OEM Pack" piece of foam (with anti-static bags) may be the best option. Better, consider putting the whole mess into a media-rated fire-safe.

Well, if you're going to pull a big Cat6 (or whatever) run and then crip ends on it, it doesn't matter if you're building or buying - it's not the right way to be installing the cable.

For a long run like that you should be terminating both ends into a patch panel of some sort. Mount the cable and panel securely - the solid core cable that you're probably buying isn't designed to "hang loose". I'd strongly suggest you run 2 or 4 cables at the same time. Cable is relatively cheap, labor isn't, even yours. This way when you change vendors, get another circuit, etc you'll already have teh run done. It also gives you an easy way to check if it's a cable issue or now when something stops working.

Run the cables, patch panel on each end, then factor-made stranded-core patch cables from teh panels to the endpoints.