Older advice was to consider adding L2ARC starting at 64Gb of RAM. You would go by the ARC statistics to see if you have a low hit rate that adding L2ARC would help. The L2ARC needs to be faster than the storage pool to assist. If you had fast NVMe storage for your data VDEV & Pool, the L2ARC isn’t as helpful if it is the same speed to read from.
The other issue with your first choice for L2ARC looked to be planning 2Tb but that needs to take up RAM, that could otherwise be used for plain ARC. The memory requirements aren’t as high as they were in the past but you should start with a smaller amount allotted.
You can play with both L2ARC and SLOG as both types can be removed from the pool without having to recreate the data. (pool destruction and recreation).
A recent thread on L2ARC sizing, etc discussion
See below for Special VDEV (sVDEV) Planning, Sizing, and Considerations
