Thanks a lot Andrew, this is a gold mine to investigate all possible issues!
One may dream to buy an ADC board, with flexibility with resistors and capacitors + voltage reference (switchable excitation signal) so to cope with diverse situations BUT providing a solution to most issues (good PCB design,good connectors, EMC protection, ... ) ! In the current situation, after demonstrating a working prototype, I will be obliged to design a PCB because it will be impossible to deal with all constraints by simply assembling existing boards.
One will notice that the frequency of the measures has a deep impact on an ADC board design. Anyway Python is not allowing very high speed: probably sub kHz would be a big slice of the market.
Have a nice day !