CryBaby

I haven't seen modules like those before but I've used the typical 'terminal server' in a metal box. They work, the only caveat I would mention is that they can have old and non-standard web interfaces for configuration. Some of the cheaper ones I've used can only be accessed with Konqueror, not Firefox or other more common browsers. I don't know about VLANs.

I would look at mraa and upm.

You should ask on the kiauh github, I think the problem is kiauh not armbian.

The last time I tried using my Cubieboard 2 I wanted to use SPI and had some trouble. This was 2 or 3 years ago. The main reason I gave up though was the 2mm pin spacing. Maybe you found a suitable cable. I would start by getting a current uboot on to it then watch it boot on the serial port. Inspect the default env, see what env file it is reading, check it is loading the overlays etc.

I don't know how it works but in my experience it does. The Prolific page here says "Flexible signal level requirement on the RS-232 like serial port side also allows the PL-2303HX to connect directly to 5V, 3.3V, or 2.5V devices."

I think the one you have will be fine. Just don't connect the red wire, even on boards which have 4 pins.

If /boot is not already a separate partition I would think there is not much advantage in making it one. The main problem is machines that need a FAT formatted boot partition, as FAT is so fragile. I don't know if your Tinkerboard is one. If /boot is on an ext4 partition then fscking at boot is going to be adequate protection in most cases. If you really want to mess with your partitions I think you will have to understand the boot process of your Tinkerboard in some detail. Does boot have to be the first partition? What filesystems are acceptable? What files need to be in it and what should they contain?