Using iMovie Projects on an external SSD & a separate external Time-Machine Backup

I have recently started using iMovie to consolidate & edit a lot of old home movies. I think I made a mistake buying a 2022 M1 Mac (running Sonoma 14.5) with only .5TB of SSD memory (& only 8GB RAM), and have found that movies & movie editing takes a lot of memory storage space! So, in 2022 I originally added a new 5TB Seagate hard drive for time-machine backups and storage of ~250GB of genealogy files I've collected over 10 years. Recently, I heard that a time-machine drive should not be used for separate file storage, as the other files may be corrupted occasionally. This has created a lot of angst for me now as both the genealogy files & family home movies are very important! So, I have added two 2TB LaCie SSDs and I am trying to figure out how best to set these all up for a) external storage, b) potential file sharing with my sons (using PCs), and c) security of backup. Here is what I am thinking I will do & I'm looking for help/suggestions:

1. 1. Leave one 2TB SSD with the default Ex-FAT format, so I can share it with my son's PCs. I'll use this for the original sources for my genealogy files, source family movies & sharing of iMovie final output files.
   2. Re-format the other 2TB SSD to AFPS, so I can move the iMovie project library to it. That way I can keep all of the original iMovie projects I build, for later use.
   3. Continue to use my 5TB External Hard Drive for system backup - add the 2 external 2TB SSD drives to also be backed up by time-machine. (I also use this drive to store a time-machine backup from a MacBookPro that I have - also running Sonoma 14.5.)

Here are my questions:

1. 1. Does this plan provide at least 2 copies of all my data, on at least 2 media locations?
   2. Can I "mirror" the 2nd 2TB SSD Drive (AFPS format) with the 1st 2TB drive (Ex-FAT format), to provide two copies of the critical data with a 3rd copy in the time-machine backup? (I think that the iMovie project library will not copy to an Ex-FAT format, but how do you tell the mirror routine properly "skip" it?)
   3. I am very concerned about security of backup, but really don't want to invest in a 2TB+ cloud subscription. Does the Apple OS provide any "warnings" or status on the "health" of the external drives? I'm a little concerned that in 10years of using my Macs (with an external backup drive), I've never seen any external drive health warnings or information. Any available Apple App for disk health monitoring? How do I know if/when the time-machine copy of my data might be corrupted? (My worst nightmare is I go to look for an old copy of my files, and I find it is not available or not readable.)
   4. I think only the iMovie SSD might benefit to be high speed, so only it and my 5TB time-machine backup drive will be on the 2 available "Thunderbolt" interfaces. I'll plan on using one of the other USB-Cs for the 2TB SSD Ex-FAT drive (sharing drive). That leaves a single USB-C interface for occasional magic accessory charging, USB-C Thumb Drive, iPhone, or iPad connection.