Mechanical Hdd Lifetime

Speaking generally to heavy HDD usage rather than chia specifically... Mechanical HDDs shouldn't see much lifetime shortening from heavy use if they're kept cool, but you may see issues that lie dormant for years on lightly used HDDs become visible sooner with heavy use
You can do stuff around an SSD or RAM caching tier in front of mechanical disks to accelerate things, tho I'd suggest using Enterprise grade write optimized SLC NAND if you do go with SSD to make it last a lot longer, but you'll still have to treat the SSD as a consumable.
If you can afford it, battery backed RAM caching is awesome