I eventually used a level shifter 3.3V to connect to my Arduino nano and that unknown library. Now it works fine. The list of obstacles to obtain full functionality was however to long to my taste :-).
On long run, I also plan to go for 3.3 C Arduino boards. NodeMCU looks great (I didnt touch one ever, but from the specifications and taking into account the microcontroller that seems to be very respected). With my precarious knowledge, I wont dare to use the wi-fi connection, thus that part may remain un-used. Taking into account its reasonable price, its un-used (but paid) wi-fi part may not be a problem, in my case.
Now I am on 5V Arduino nano, manily because my start on Uno - great piece to learn, BTW! I have a genuine Arduino UNO one.
Indeed, tinkering lots of connections generated by a level shifter, a 3.3 Board is a more workable alternative. The only point which I wonder about a 3.3 V board is how to power it externally. One solution appears to be 1 x 18650 Li-Ion battery connected straight to the board. If alkaline piles are used, then I guess it will take 3 of 1.5 V + a regulator to 3.3. V. Not sure, just my first impressions, I have no idea how most people power the 3.3V boards.