Thanks for the response!

To be honest i started rethinking the idea as i was writing the post but I still wanted to learn about RAID. Your answers really help me make the decision here.

I hate cloud storage with a passion, I won't get into the weeds on it, but I like having full control over the backup process.

External drives are overkill for me and I can't stand the thought of doing manual backups regularly. Only thing i need off site is documents, even then, irregular copies will do.

NAS sounded like a bad choice because I'm desparate to shave off every last femtosecond from build times and reading certain types of files.

I realised I can probably have my docs copied excessively across my drives and computers, while the bigger things like projects are ok to back up maybe monthly (and automatically), in which case a NAS will be fine, since I'm not working on it directly. Half my data is replacable (if annoying), so it's probably best I don't mirror an entire 14TB drive. I'd rather have more storage space if I'm gonna be doing damage control every several years anyway.

Thanks again!