I've had this happen a couple times, and contacting the seller directly has gotten it sorted out. Even if they seem sketchy, they don't want to take a hit to their reputation. If they don't want to help, I'd escalate to eBay support.
If neither of them work out, then I'd try contacting WD. A refurb with no warranty is better than nothing at that point.
A Zero would probably be way underpowered for the job. I've used a Pi 4 in the past and it worked ok, but choked occasionally.
My actual recommendation would be a small x86 box, something like a Lenovo Thinkcentre Tiny. You can get them used for about the price of a Pi, and they'll be much more reliable.
A lot of US banks also have that as an option, people opt in to "overdraft protection" anyway. The banks make it sound like a safer option, instead of the predatory practice it normally is.
Automating updates is generally frowned upon, that's when things can break. But waiting to run updates until you feel like it (instead of daily) is totally fine. I've been using Arch and its forks for years, and have always updated once a week unless something was wrong.
EndeavourOS or raw Arch would both fit that bill, you don't need to run updates every day just because they're available. Manjaro delays packages to "increase stability", but that's what causes it to break.
Caller (Phone) has a package available on their github you can grab now, and f-droid should recognize the install once it hits the repos. They're releasing pretty quickly, all things considered.
The Fossify forks of simple apps should be coming soon too, if you want to stick with something familiar. They've already released their calendar, gallery, and file manager, the rest should be ready pretty soon.
For a NAS, you're usually concerned with capacity first. And you can't buy a 20TB m2.