SoftRAID has many features that improve the RAID system. For example, you can optimize the system for general workstation, server, digital video, digital audio, or digital photography.

While you're gathering data, I found the discussion of RAID from OWC to be quite useful, especially the sections on Levels, Uses, and Options. For example, RAID 1-0 is about 30% slower on writes than RAID 4 or 5.
https://www.softraid.com/raid/

In looking at items in their news section, a couple of other things I didn't know:
-- When you get an OWC system with the drives, they do a full certification of the drives before shipping. That is, they run the full certify process for every drive, checking read/write for every sector, which takes 1 to 2 days. The SoftRAID app can do this also, which they recommend for new drives if you buy them separately.
-- SoftRAID can also certify SD and other cards, which helps alert you if a card is starting to fail. Good to know before a photo shoot.
-- SoftRAID is integrated tightly with the macOS kernel, making it very efficient for reads and writes.

SoftRAID shows data on the hours of use, I/O errors, and SMART status (general health), which can help indicate when a drive is nearing the end of its life before it crashes. A SoftRAID icon in the task bar turns from blue to yellow or red if there are any errors. Here is a screenshot showing some of the error checking in SoftRAID on my system.

all the JBODs I’m familiar with are enterprise/commercial grade and not cost effective for personal use unless you pick up a used one. Perhaps someone else has bought a consumer grade (with a fan) recently and can recommend. Pick one with an interface that matches what’s available on your Mac, and buy more slots than you need right now, both for a spare and future expansion. I do recommend you buy enterprise class drives such as the HGST/WD UltraStar - well worth the extra $ for the reliability.

Once you choose your HW and the number of drives we can discuss the optimum RAID level for speed and resilience. You may find this post on Apple useful: https://discussions.apple.com/thread/252494089

RAID is not specifically for backup. When properly implemented, it does provide redundancy and downtime reduction, but not backup in the traditional sense. If you need to have full time 24/7/365 access to your data with no downtime, RAID is great. As far was what level of RAID, I would not suggest anything less than 0+1 or 1+0. No one who cares about their data would implement RAID 5. It is slow, only has one drive for parity, and changes to the striped drives require an update to the parity drive, which diminishes its fault tolerance and overall performance. In a RAID 5, if one drive faults, the remaining two drives are completely vulnerable until the failed drive is replaced. In the other schemes there is double redundancy, therefore better fault tolerance. I would avoid software RAID for performance and reliability reasons.

However, neither of these provide a backup solution per se. Good backups create historical data sets, so if something goes wrong or gets corrupted you can go back several generations to get to the last version of a file before the fault. For efficient disk utilization, backups should be incremental, ie, only files that have been changed/added are actually copied. You don't need to make a complete copy of an entire drive to consider it backed up, so technically, you could use a smaller drive to back up a bigger drive, as long as the data being recorded is not bigger than the smaller drive. The drive capacity is not a factor here. There is a lot to know about backup, and unfortunately you are not likely to come by people who actually know what they are doing and will likely give you well-meaning but potentially dangerous advice. At the end of the day, your backup should have 3 copies, 2 of them local on separate devices, and one in a remote location.

A mirror image of your system drive should also be made periodically, in the event of theft, fire, flood, catastrophic failure, etc. so that you can rebuild the system drive to a similar computer. The issue of data security can be a rabbit hole, but one that anyone who uses a computer needs to venture into on a regular basis.