For what it is worth in the NAS:
20x 6TB HDD - $1,400 ($11.66 per TB)
10 x18TB HDD - $3,500 ($19.44 per TB)

Hopefully deals like these can keep the cost of your NAS down a bit

Why are you using third party tools for this?

An “unreadable” result sounds like a failure from HashCheck - What does your OS Native tools give you?

How storage do you need?

Absolutely, copy the source.

Internet Link Rot gets worse every day

Probably identical to a Seagate Exos with a 400% Dell Markup

Seagate has 32TB HAMR coming out in the next ~7 months

Sir, this is r/DataHoarder