The only issue is that NAS, not because I have any experience with it, but because I’m not sure I trust non-local solutions with Time Machine. It’s just not designed to work over a network—it has no client/server architecture—so interruptions are likely to cause corruption.
Dave Hamilton mentioned a workaround at MacTech Conference last year. If I remember right, the idea was that you could back up via Time Machine to a NAS using the btrfs filesystem, which allows regular snapshots, much like APFS. Then, if you had a Time Machine problem, you could revert the Time Machine backup to a previous snapshot to avoid any potential corruptions problems. I’ve never tested this, or even had a NAS, but it’s worth considering.
I do feel that bootable clones need to be on SSDs now, if you really think you’re going to boot from them and try to get work done.