Ah I get it.
Anyway low consumption kind of mandates that kind of flash build IMO.
Isn't there any way you could stagger buying those SSD? Like you buy them one by one only on sales or refurbished hardware.
You could also maybe attempt a raid5 only with only 3 disks until you could buy a fourth one?
Anyway good luck!
I dont really have the time to participate in what looks like an interesting debate but I have a few notes on your post.
Secure what? Against what type of threat? This type of vague question results in vague answers. If the threat is social engineering I would argue not many protection would be effective beside educating the user about that.
You don't stop them. You ask them and show them a disclaimer when they activate sideloading and that's it. They are on their own. If the user doesn't understand the risk after (skipping) the disclaimer. That's their own fault. I don't want to be put in prison just to make sure nothing bad ever happen to me. If a user purposefully disable protections they are on their own. But they should always be able to disable them.
This is the openness of the OG Android. Welcoming as many users as possible even if they are not your mean average user. It doesn't matter if these user are a minority. They should be able to override any security they want. As long as they have acknowledged that they understand the risk and will not sue Google for it. I don't see the problem.
I have worked on a custom ROM based on AOSP and that's the other trend that worries me. The fact that less and less of "Android" seems to go to AOSP was already a concern years ago. Google wants to close their OS to better compete with Apple. This means severing those annoying minority power users from the rest of the community.
I see a very paradoxical response from you coming from Linux. If you enjoy Linux for its openness why would you accept Google rhetoric like that is really surprising. Let users do complicated stuff on your software as long as they have signed a virtual "I AM IN DANGER" form that's OK. If you remove these advanced settings features anyway then it's not for the user, it's a PR move to protect the perception of your software.
Sorry if this comment seems a bit aggressive. In my opinion you are arguing for Android to slowly transform into IOS and ad someone working on Linux for decades, this is very weird.