This is how I do it. No striping, normal partitions, different hard drive sizes, pretty easy. This way makes upgrades super easy too. Currently running 76TB mergerfs with 2 14TB Snapraid parity drives.

Probably not that deep. I've heard there are definitely discounts. That doesn't count for much though when it still increases your cost 6x.

This honestly sounds like the best solution to this particular problem.