Thanks, Jlmr731!

I am finally starting to get a better understanding.

I have 1 PCIe x16 available, sorry for not mentioning it earlier.

So if I get this card (or this one, or) along with these cables, is it all I need to make it work?

okay, from what i'm reading about the sas2-EL1 backplane, I'm going to have 1 SAS connector, but does that make sense based on what you're saying? I definitely want 24 drives available for use.

StorageTekPro - LSI 9300-16i 16-Port 12Gb/s SAS Controller HBA Card with P16 IT Mode for ZFS TrueNAS unRAID

Would this work? I'm assuming 2 will get used for the current set up, and then i have 2 open ready for a disk shelf addition in the future?