Couple of thoughts on this, firstly your backup, as EsaT said ...no, don't do it that way, for backups you want to do it to something that is seperate to your machine and not connected to it all the time, so either a different system entirely, NAS or whatever or really the best and simplest way for most people is just use an external hard drive, connect it to backup and then disconnect it. This is what I do, plus I have a copy of that hard drive I update every month or so (my important files don't change that fast generally) I keep at my mothers house.
If you want scheduled backups nightly then you're gonna need to backup up to another system that's up all the time of course, a fileserver or NAS ideally but I would still be weary of that to a point for a couple of reasons, if it's permanently running off the same power as the rest of your house it could suffer in the event of some sort of transient event, a good PDU with battery backup will help here, however in the event of fire or flood though ...not so much or a disaster like that it's worth thinking carefully if you should keep anything 'offsite'.
Also one you can configure your way around and a lot of people don't consider is the possibility of simple network exposure, for example if the backup location is easily accessible from your desktops via the LAN you could fall foul of a virus than encrypts not only your files on the infected desktop but also spreads and gets all your backups aswell ...I'm kind of painting worst case scenarios here but that's also part of my job being involved in running data centre operations for a software company so ...just bear this in mind, how secure do you really want those files to be?
If it's just a convenience thing you can tier it, so have a nice fast backup to another system in your house so you can restore your system quickly if you need to, but have a more secure offsite file backup to public cloud for your really important stuff perhaps. This can take a while to do an initial upload of but unless you are cranking out a lot of file changes should be quite manageably to sync to after the initial upload, however do bear in mind the encryption virus scenario still with this if it's just permanently syncing to cloud storage from your desktop, it's always best to have an offline copy somewhere.
Next thought is more of an observation as to the way I see hardware and software developing at the moment, I think the time of keeping a system for 9 years has passed now, I seriously doubt we will see that again for a while and if you wanted a chance at that you'ed need to be looking at something more like a Ryzen 5950X I reckon. I think 5 years will be a more reasonable expectation given the pace of development has picked up a lot the last 2 years but I don't see it being quite like the '90s and early '00s where you were thankful to get 2 years.
Finally, a technical thought, I 'believe' a Z590 system is only going to give you PCIe 4 support to a single M2 slot, usually the top one nearest the CPU. Bear in mind you only have 20 PCIe lanes direct to the CPU, 16 for the GPU and 4 for a storage device is typically how they are divided. Everything else will need to run through the chipset and without going away and doing some reading I am not sure that supports PCIe 4 on Z590 ...in the AMD world you need X570 for that as B550 can't do it either. As I say not 100% sure on this scenario with Z590 but I would be careful here, I would not be surprised if you can only use 1 PCIe 4 storage device and then have to drop down to PCIe 3 for the rest via the chipset.
Edit: I did some reading for you as I was curious, yes I was right, you're only going to get one nvme gen 4 storage device to work with a Z590 system ...unless you use a PCIe 4 nvme expansion card in your top PCIe slot so you can use the GPU lanes for it.
The chipset lanes of which there are 24 are PCIe 3, so given the limitation is actually the DMI link from the chipset to the CPU here not the total number of lanes, you actually have enough bandwidth theoretically to run 2 x nvme gen 3 drives at full speed off the chipset.
Have a look at these articles if you want to have a look for yourself.
https://laurentschoice.com/2021/tech-news/4782/
https://techteamgb.co.uk/2021/01/29/z590-explained-pcie-gen-4/