What to use to store essential data for home users on NASs. Single Drive vs JBOD vs Raid 10 vs Raid 6 vs Riad 5

The biggest down side to RAID (vs JBOD) is expense. In my experience raid will cost you double or tipple what JBOD does in time and materials per GB. Raid card gets damaged you need an identical one to replace it, motherboard taking care of your raid, now you have to install a new motherboard. Was information on the array damaged (garbage in) due to the raid adapter failure (I've seen it a handful of times), better hope you have a backup of all the data cause it's all gone regardless of what level you're running, if you don't have a backup of the information you can spend $2600+ to have a data recovery center pull the files off the full array with specialized equipment over the course of a week (or three depending where you are and where the lab is and how backed up they are). Do you want to add more space to your array, JBOD is easy, put it in and you have the space of that drive added to your total capacity regardless of size, if you try that with RAID and you want your monies worth you must have an identical HDD (or two in some cases).
JBOD isn't the beez kneez but if cost is what is most important, RAID can screw you bad if you're unlucky (unluck increases over time, give it enough time and we'll all be unlucky).
The benefits of RAID are speed in most cases and data redundancy in lucky cases. Take it from a guy with repair experience JBOD with a backup of the disk array is more reliable for the $ than any RAID array (and in a select few cases is even better performance, (almost always so for small random reads and writes even over RAID 0). JBOD also happens to be better with individual disk longevity that only increases with the number of drives present in the array.

If I were in your position I'd get a NAS like the the synology with JBOD or individual disks per user you mentioned but only use it as backup while keeping the primary files on the individual machines that way you're not at risk of loosing your files in anything less than a fire. Make sure you buy WD BLACK HDD, in my experience they are about 50% less likely to go bad compared to the competition or other WD drives. The reason I suggest NAS over USB external HDD is because external HDD's spin all the time even when not in use and that wears them down and can even over heat if they're in a bad location or if it is a cheep external enclosure. Also external HDD's have to be plugged in to do the backup and that requires effort - most of us are to lazy to make the effort to do regular backups while NAS systems are great with automated backup software. Also there are many NAS systems available with 2-4 or even 8-12 drive bays with many configurations available such as a JBOD for your backup and another JBOD for network storage (for dnla streaming or shared storage etc..).

I think you are fairly well setup for the zombie apocalypse. What backup software are you using?

The only backup software I have found to do just about everything is Syncovery (Super Flexible File Synchronizer).
You are just like me and I think we both have to many drives. Our systems are complicated. Simplicity always wins
I plan on buying another Synology and using it to backup the other Synology drives. Local storage for day to day operation backed up to multiple Synology units. (BTW NEVER use green drives, they will timeout trying to fix errors and go offline, RED drives timeout quicker on bad reads an allow the system (synology) to handle the error before taking the drive off line)