I think you have gotten a bunch of very good advice.
My backup strategy incorporates the idea of 3-2-1, but rather than the “2” standing for “2 different media,” which I think is no longer really an operable approach (it was when we had small enough amounts of data that a CD or later DVD could be a backup, but today, backup pretty much means to another hard drive), for me the “2” means two different methods of backup.
- TImeMachine is the first line of defense, because it is built in to MacOS, is therefore relatively easy to set up, and for the most part will allow you to step back in time to retrieve a selected earlier version of a file and/or restore an entire system. The downside is that TM is often glitchy, and very few Mac users have avoided the experience of being informed that their TM backup is not valid and having to restart the whole thing over, thus losing all of the previous versions. My sense from watching this over the years is that this is more common when TM is to a networked drive than to a locally attached drive, but that may be reporting bias.
In any case, I don’t think it matters a whole lot if your TM backup is to locally attached drives or to a networked location such as a Time Capsule, NAS (Drobo, Synology, QNap, etc), or another Mac that shares our a TM store.
Since you are both working on laptops, the Time Capsule makes more sense for your specific situation, because then the TM backups can occur without you having to remember to physically hook up the drive.
- My second line of defense is a clone. The advantage to a clone is a complete replica of your currently working system (as of the time you did the clone, of course). A big advantage of a clone is its ease of use in restoring a working system, and as others have noted, if one of your laptops dies, you can connect the clone drive to another laptop or other Mac, boot from it, and you can continue working while your primary system is being repaired.
Again, I have a lot of redundancy in my own system. I use Carbon Copy Cloner, and both my MacBookPro (my only working computer) and my Mac Mini Sever each make two clones. One is made daily to a Drobo attached to the Mini. The other is made to a directly attached USB drive and is a bootable clone (note that clones to a NAS are NOT bootable directly) to address the issue above. I use CCC’s feature of archiving deleted files so I can go back and find previous versions of changed files and/or deleted files if needed. Disk space is relatively cheap and I have enough room on my Drobo used for the clones to be able to keep things more or less indefinitely. As least, so far.
My laptop plugs into a Thunderbolt 3 dock when I am using it at my desk, and the bootable clone is attached to the dock, so a new bootable clone is made when I do this hookup, which is usually just on weekends. However, it also clones to the Mini over the WiFi any time I am using it at home on other days as well. My bootable clone is thus as much as a week old, but enough for emergencies, since I also have the TM backups and my cloud backup - see below.
- I also feel strongly that all important data should be backed up somewhere on the cloud. I am not a fan of the idea of making a clone periodically and swapping drives with a trusted person or safe deposit box or whatever, because I want my offsite clone to be, at all times, very close to current and something that happens without manual intervention. Having it be dependent on me swapping drives with an off-site storage site is just not a good plan.
I use Arq for reasons I have noted elsewhere on the forum: BackBlaze will delete any file that you have deleted after 30 days. I have had the situation of finding out 6 months down the line that I inadvertently deleted files I wanted, and since I had Arq (then going to Amazon Glacier) I just restored them…which BackBlaze would NOT have allowed me to do. I now use Arq to BackBlaze B2. Yes, it costs me a bit more (I have 2TB in the cloud) but it’s worth it to me. Plus, Arq runs every hour on my laptop, as long as I have an internet connection. My Synology shares are mounted to my Mac mini and Arq backs them up every 6 hours, which is frequent enough for those shares.
Hope this is of some help.