What you can have which I think achieves what you want is:
2x18TB in main array
500GB NVME as pool1 set to act as cache for shares on main array
pool2 with multiple spinning HD set up as RAID1 to give redundancy to be used for torrenting.
still leaves other drives free to either be added to array, or perhaps used as pools for hosting VMs and/or Docker containers.
the Unraid roadmap does talk about having multiple main arrays, but if this ever does materialise it is still some way off.