So, finally yesterday I received all the bits an pieces to try to make this work - and I did with rather very few complications.
Thank you very much, @Koenkk, for this great piece of software and the instructions on how to make it work!
I now have 2 Aqara temperature sensors connected and am already thinking about many other uses 
One quick question to the people who’ve been using it for a while with these sensors:
How long do you expect the batteries to last?
I have one of the sensors in my fridge, the other one in the freezer. Both have been running for roughly a day now, but the battery-%age has gone down significantly already.
I know it’s a rough environment for the batteries, but I’m still surprised about the battery drain so far.
I also know that the linkquality values of 35ish are probably not ideal either, but short of putting the RPi in the freezer as well 
I’m not sure what to do.