You probably need to reset the configuration on the controllers. I’m not familiar with that particular unit but older ones had serial ports that you could plug in a cable to and would either have a firmware prompt for commands or a menu system that you could interact with to do things like clear errors or reset the configuration.
I use hledger mostly because of the plain text format. I came from YNAB as well but I just hated how you couldn’t easily undo changes or see when you made a change, etc. This is so easily to track changes and you can add comments explaining your reasoning around things and you can keep everything in source control so you have all the power of that as well. Not for everyone but if you’re a programmer or just comfortable on the command line it’s great.
Using the SAS cards instead of the FC controllers should be fine, but it will be a different beast. The MD3600 controllers are basically your RAID card and you use a SAS HBA to connect to it. The virtual disks are configured on the MD3600 and exposed as LUNs to the hosts over FC. If you put plain SAS controllers in the storage chassis instead, you are exposing all the bare drives to the host. That is how I would do it if I were in your shoes and then would just create ZFS arrays over those bare disks. If I were going to try and have multiple hosts using that storage then you would need to stick with the MD3600F.