I would jump at the better speed for less money.
Depending on what you need the IP for, you can bypass CGNAT with DDNS and other methods reliably and easily.
Not enough for a mid-level office/enterprise, but sufficient for everything below. Barring extreme homelabers.
This would work but backwards.
Since system 2 is the one with the raid/HBA card I assume that would house your brains.
Looking at the end-product, 16x SATA connections. It would be a waste of cables/money to do it the way you pictured.
It would be sufficient to run a single 4e 8644 port from system head to JBOD, there you could use an expander to achieve the 16i needed. This way you would have 6Gx4=24G/3GB or ≈250MB per drive. Could do the same with 8e, point is you are maxing out the 12 drives with 4e don’t need 16e and associated cables.
Depending on your future needs you could go with 8e/16e in the head and have those extra ports in case in the future you want to add another JBOD (1 per 4e).
PS since you head appears to have drives, you should source an external card from the get-go instead of an internal to then connect cables to an external converter. I’m assuming you pictured an additional card and not the one running those disks.
Hope that was clear enough.
🍻