cache Pool size

Hi im in the process of building a unraid server ,, which im totally new to. Im sure this has been asked loads of times but would be the ideal cache pool size for me. I will be intially starting with 3 16 disks in raid 5 and adding more as the need for more storage arises.Ive got a case that will house 8 disks so the eventual useable storage will be around 101tb. The server will be mostly used for storage and plex and running a few vms(not as daily drivers though). In terms of dockers i will be using Plex and Handbrake for sure ,  will need to see what other dockers are available.Intially ive got around 4tb worth of movie files to move over from my main machine after that the data transfer will be significantly less Will only add data when i need to .I  got 1tb nvme for the cache drive with a 500gb sd for the OS but i realised today thats not how it works so im thinking of returning both and replacing it with a 2tb drive. ive got two nvme ports but the other will get occupied by a sata controller so i wont be able to add more storage unless i swap it over a bigger drive (waste of a drive) or invest in an expansion card that will house addtional nvme(no plans to do this just yet). Do you think 2tb nvme will be a good option for me.