Right now my goto basic chunk of block storage is WD 8TB Blue drives. Brand new out of the box price per TB is hard to beat in my area, and they’ve been shockingly reliable and performant.
I see the price of NAS drives and frankly don’t see how they could be worth the price is you follow sound backup strategies.
Literally any drive. If you don’t want to lose data, then make sure you have backups because all drives are prone to failure at some unknown point in the future.
20TB of usable storage means at least 60TB of total storage. 20TB as primary local data, 20TB as local backup, and 20TB as offsite backup.
I still have old IDE drives (with the ribbon cables) that still work. I still plug them in on occasion to check the data on them because they hold a copy of very old cold storage data, and even though that's not the only copy of that particular data, as long as the drive still works and I have a means of accessing it, I'll still use it to store copies of data. The oldest drive I have is a western digital 4GB drive.
triple your rates. Seriously, a lot of times people don't take you up on it because you're simply not charging enough. I went through a similar thing and doubled my rates and went from struggling to get any bookings to getting more work than I knew what to do with. Do some footwork and figure out what the going rate is for your area and charge the same amount or maybe a little less.