Port to devices without any basis?

[jojumaxx]

I started to read the guide about porting and as I understand some basics must be given, like TWRP recovery to enter the device, vendor blobs, etc.

I got e.g. a Gigaset ME Pro, which was meant to be a high end device back then and therefore still has potent hardware, comparable to the Volla Phone which comes from Gigaset, too.
I also got a GS370 Plus with similar hardware and even another one.
Gigaset had many good devices, but they hardly updated the software, so the devices were outdated pretty quickly which is a pity.

However, I can't find anything that seems to be necessary to start a port. Is that possible at all in that case?
While the GS370 Plus was running on Android 8 (updated from Android 7), the ME Pro was running on Android 5 as far as I remember. How about that?

Thanks for your answers.