Build / buy pc or server for high IO

[ikatamoonshots]

I want to build or buy a pc/server for very high IO applications, anybody with experience here?
Will be hosted at home so dont have to meet any box specifics.
Where to set priorities?
What parts to buy new or used, what to avoid - cpu, mb, ram, raidcard, disks? Storage at least 15 tb
Budget is 1,5K€

thanks for any help!