What do you have in mind for all those SSDs?
SSDs in the parity array cannot be trimmed, and whether or not all models will work with parity isn't entirely clear.
And your assortment of HDDs isn't really the way I would go about this either. It is better to have fewer larger disks than more smaller disks. Fewer disks requires less ports and other hardware, and each additional disk is an additional point of failure.
Since you are just playing around right now, simplify your setup with just a couple of the newer SSDs in the cache pool and leave out those other SSDs and those old small HDDs.
How full have you made all of those disks? If all the data will fit on the 8 3TB disks, then you could just go with that in the parity array and then use the Unassigned Devices plugin to copy the data from the other disks one at a time.