I have tried to set up most of the options and I ended up on Filebrowser Quantum.

Simple to set up and use. I recommend giving it a try.

https://eylenburg.github.io/android_comparison.htm

This is a great table of comparisons between the different Android alternatives.

With 3 drives I would go with BTRFS RAID1. You get half the capacity, can lose any one of the drives, and it is really simple.

If you were to add drives later on to increase the array size, I might consider RAID10, but if you plan on sticking with 3 drives, I would go with RAID1 instead.

RAID0 offers no redundancy, so I would skip it.

RAID5/6 are not recommended for use in production.

While Obsidian is undoubtably a good piece of software

Don’t promote proprietary software!

Self host filebrowser quantum! Small, light and easy to configure.

It is currently in beta, but it is on the cusp of a stable release.

PostmarketOS has piqued my interest as the most promising Linux phone OS. I would give it a try if you can put up with an immature system, at least when compared to Android.

Need a source on this one, I want to read up on this.

NovaCustom: Coreboot, Linux support, customizable, spare parts.

I have no personal experience, but their products seem nice, though expensive.

https://novacustom.com/