This is a demo store. No orders will be fulfilled.
ZFS can benefit from a ZFS cache, on the Motherboard we sell there is a M.2 socket free, so you could add a single PCI SSD. But the write cache needs to be mirrored, to prevent data loss. You can add a PCIe to M.2 card in the free PCIe slots.
You can choose between TLC or MLC. The TLC are cheaper, the MLC more durable(for writes). You can also take a bigger TLC vs a smaller MLC. You have more cells vs longer durability.
There is no short answer which one to choose, if budget allows please take the MLC SSD. And always mirror your ZFS intent log (ZIL).
And please monitor your wearout factor on your SSD with S.M.A.R.T. (Wear_Leveling_Count).