Thank you, but I tought of the more complex method because of
Maurello:
some different uses and space problems
So if I need to connnect four of them in series with my method I think I will have more flexibility (every module is identical and can connect with every other with no specific order), instead of having different modules that can connect in just one way: the closest to the 4051 will have one output (connected to the 4051 input Y0) and three extensions, the second one will have one output (connected to the extension on the previous module which is connected to 4051's Y1 input) and two extensions, and so on.
This if I understood correctly how the 4051 works: I have to send the digital values to the select pins (A0-A2) from the arduino's digital outputs, it can't detect itself which input I'm activating as the encoder does.