I'm using the partitioning tool of the installer (which under the hood is gparted anyway ) to manually set partitions for /, /boot, /usr, /etc, /var, /tmp and /home. By limiting the size of these directories any rogue process triggered to fill up as much space as possible cannot make the system unstable or even unbootable.

The answer is there, first post, several times even:

apt --fix-broken install

Here's the Brother support site:
https://support.brother.com/g/b/product … content=dl

Select your region, model, follow instructions and you should be able to get a download link to the installer. That's just a script selecting the correct drivers for your device and installing them.

FIY: my last 3 printers (actually MFC units) were all Brother products due to their excellent Linux support. Current machine: MFC-J5740DW (no WiFi configured, so no access from outside )

Nobody ever got fired for buying a Dell. Same goes for HP, IBM and Lenovo.

Despite having my daily driver PC on AMD hardware for the past 25 yrs, I'd suggest you'd hunt down an older workstation (Intel 10th, 11th or 12th gen CPU) for cheap, maximize RAM, add 2-4 HDD's for long term storage in RAID 1, 5 or 6, a 1TB NVMe SSD for the OS and any VM's you'd like to run.

As for the OS: Although Devuan can do all the tasks you planned for, I'd suggest being practical and consider specific NAS-OS's like HexOS, TrueNAS Scale, UnRAID or ProxMox instead. Yes, they use systemd and as much as I despise it, realistically that's not going away anytime soon. As your only online portal for your community, downtime due to having to tinker with a manual Devuan setup isn't really acceptable. You'd also need to consider online risks: you may not consider your community a target, online criminals will have a field day hacking your machine and turning it to making them money whichever way they want. Devuan simply doesn't have a GUI tool that makes configuring it suitable for online use, like HexOS is for TrueNAS. The project lacks the resources and realistically, it's not gonna happen anytime soon, even if someone steps up developing the required functionality for it today.

Touch screen support is basically a driver issue in the kernel these days, chances are it'll work out of the box if the particular touch module can be loaded. Probably not easy to find, but see if you can get your hands on the apple tech specs for those devices, then google the touch screen model for compatibility in Linux. If that module is already in the kernel, you're in business and the Devuan installer should recognize it straight away. If the module exists but isn't automagically loaded into the kernel, you may try loading it via the initrd image for your particular kernel. Not recommended for novices, but with guidance still doable. If there is no module, and you can find the actual drivers, you can build and install a module the kernel can use. This gets tricky even for experienced users, but you can still pull it off, taking your time. Worst case, there is no driver (which I'd doubt as apple OS is a BSD variant so there should be) then you're screwed and you'd have to write your own. Unless you're a Linux dev with experience, don't go there.

HTH!

The actual problem is that fsck wants to scan an FS already mounted. You can unmount swap and have it checked, but as you're reselling the machine, just re-install Linux afresh and be done with it.

I disagree. If you have a login, just log in and your theme will be applied. Don't force your personal preference on guests.

Just me tuppence

Once you figured out which files are safe to delete, it's a small step automating this in a script. Which can then be packaged as a .deb for anyone to install as they see fit.

Just a thought

Hoping to make a useful contribution to this thread!

None of this has anything to do with Google potentially loosing Chrome

Some hardware options:
https://www.amazon.com/isbn-scanner/s?k=isbn+scanner

Never tried myself, so YMMV!