Whatever you choose as a storage device have a second device of the same capacity as a backup. I helped manage personal computer systems for a large publishing company and part of that job was doing grief counseling for people who never backed up their work. It's not a question of whether a hard drive will fail, it's when it will fail. It will fail eventually.
My digital library is about the same size as yours would be, with the addition of a couple of thousand photographic images, and I have three backups. One is kept in a waterproof, fireproof safe that itself is inside a locked metal cabinet designed as a gun safe. Another is kept at my daughter's house. With an inexpensive program that does incremental backups, keeping current with the backups is a painless process.
My digital library is about the same size as yours would be, with the addition of a couple of thousand photographic images, and I have three backups. One is kept in a waterproof, fireproof safe that itself is inside a locked metal cabinet designed as a gun safe. Another is kept at my daughter's house. With an inexpensive program that does incremental backups, keeping current with the backups is a painless process.