1 big SSD or multiple? New NAS build.

I'm looking to spec out a new NAS. I have a relatively small media collection, that I hope to grow as I digitize more family VHS tapes etc. Right now I have around 4 TB of data, shared across an external drive and my internal ssd.

Whats the best path forward on drives in this new NAS? I've heard advice for buying one big 20TB drive over multiple smaller drives. What's best for mitigation of drive failure? Is that even a concern? If I do multiple drives, should I use RAID?

I'm a little new to this. If you have resources for learning some best practices I'm all ears.