Cache drive size for 40tb+ download queue

I am currently running a Samsung pro 2tb nvme SSD. All my remaining m.2 slots in my motherboard are full so I cant simply add another.

My download queue is massive which will of course continuously fill up the cache which will trigger mover and then my downloads start to get throttled.

I am thinking to upgrade the nvme to a 8tb drive which will take a lot longer to fill up and my spinning drives will not get hammered as much. I know mover is going to take even longer given the amount of storage that will need to be moved.

Given this would it be worth upgrading I know once the downloads are finished 8tb is going to be completely overkill but I could use a Plex cache mover maybe? However im not sure how that works if the drive fails. Also if it is worth doing how can I simply replace the cache drive with a trashlists file system setup Data >